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Unformatted text preview: 9160335_CH01_p001030.qxd 6/22/09 8:55 AM Page 1 PA RT ONE Introduction 1 What Is Economics? After studying this chapter,
y ou will be able to:
■ Define economics and distinguish between
microeconomics and macroeconomics ■ Explain the two big questions of economics ■ Explain the key ideas that define the economic way
of thinking ■ Explain how economists go about their work as social
scientists You are studying economics at a time of extraordinary change. The United States is the world’s most powerful
nation, but China, India, Brazil, and Russia, nations with a combined population that dwarfs our own, are emerging to play
ever greater roles in an expanding global economy. The techno and seize the opportunities they present, you must under logical change that is driving this expansion has brought us the stand the powerful forces at play. The economics that you’re laptops, wireless broadband, iPods, DVDs, cell phones, and about to learn will become your most reliable guide. This video games that have transformed the way we work and play. chapter gets you started. It describes the questions that But this expanding global economy has also brought us sky economists try to answer and the ways in which they search rocketing food and fuel prices and is contributing to global for the answers. warming and climate change.
Your life will be shaped by the challenges you face and the
opportunities that you create. But to face those challenges 1 9160335_CH01_p001030.qxd 2 6/22/09 8:55 AM Page 2 CHAPTER 1 What Is Economics? ◆ Definition of Economics
All economic questions arise because we want more
than we can get. We want a peaceful and secure
world. We want clean air, lakes, and rivers. We want
long and healthy lives. We want good schools, colleges, and universities. We want spacious and comfortable homes. We want an enormous range of
sports and recreational gear from running shoes
to jet skis. We want the time to enjoy sports, games,
novels, movies, music, travel, and hanging out with
our friends.
What each one of us can get is limited by time, by
the incomes we earn, and by the prices we must pay.
Everyone ends up with some unsatisfied wants. What
we can get as a society is limited by our productive
resources. These resources include the gifts of nature,
human labor and ingenuity, and tools and equipment
that we have produced.
Our inability to satisfy all our wants is called
scarcity. The poor and the rich alike face scarcity. A
child wants a $1.00 can of soda and two 50¢ packs
of gum but has only $1.00 in his pocket. He faces
scarcity. A millionaire wants to spend the weekend
playing golf and spend the same weekend attending a
business strategy meeting. She faces scarcity. A society
wants to provide improved health care, install a computer in every classroom, explore space, clean polluted lakes and rivers, and so on. Society faces
scarcity. Even parrots face scarcity!
Faced with scarcity, we must choose among the
available alternatives. The child must choose the soda or the gum. The millionaire must choose the golf game
or the meeting. As a society, we must choose among
health care, national defense, and education.
The choices that we make depend on the incentives
that we face. An incentive is a reward that encourages an
action or a penalty that discourages one. If the price of
soda falls, the child has an incentive to choose more
soda. If a profit of $10 million is at stake, the millionaire has an incentive to skip the golf game. As computer prices tumble, school boards have an incentive to
connect more classrooms to the Internet.
Economics is the social science that studies the
choices that individuals, businesses, governments, and
entire societies make as they cope with scarcity and
the incentives that influence and reconcile those
choices. The subject divides into two main parts:
Microeconomics
Macroeconomics ■
■ Microeconomics
Microeconomics is the study of the choices that individ uals and businesses make, the way these choices interact in markets, and the influence of governments.
Some examples of microeconomic questions are: Why
are people buying more DVDs and fewer movie tickets? How would a tax on ecommerce affect eBay? Macroeconomics
Macroeconomics is the study of the performance of
the national economy and the global economy.
Some examples of macroeconomic questions are:
Why did income growth slow in the United States
in 2008? Can the Federal Reserve keep our economy expanding by cutting interest rates? Review Quiz ◆ Not only do I want a cracker—we all want a cracker! List some examples of scarcity in the United
States today.
Use the headlines in today’s news to provide
some examples of scarcity around the world.
Use today’s news to illustrate the distinction
between microeconomics and macroeconomics. © The New Yorker Collection 1985
Frank Modell from cartoonbank.com. All Rights Reserved. Work Study Plan 1.1
and get instant feedback. 1
2
3 9160335_CH01_p001030.qxd 6/22/09 8:55 AM Page 3 Two Big Economic Questions ◆ Two Big Economic
Questions FIGURE 1.1 3 What Three Countries Produce United States Two big questions summarize the scope of economics:
■ ■ How do choices end up determining what, how,
and for whom goods and services are produced?
How can choices made in the pursuit of selfinterest also promote the social interest? Brazil China What, How, and For Whom?
Goods and services are the objects that people value
and produce to satisfy human wants. Goods are
physical objects such as cell phones and automobiles. Services are tasks performed for people such as
cellphone service and autorepair service. What? What we produce varies across countries and
changes over time. In the United States today, agriculture accounts for less than 1 percent of total production, manufactured goods for 20 percent, and
services (retail and wholesale trade, health care, and
education are the biggest ones) for 80 percent. In
contrast, in China today, agriculture accounts for
more than 10 percent of total production, manufactured goods for 50 percent, and services for 40 percent. Figure 1.1 shows these numbers and also the
percentages for Brazil, which fall between those for
the United States and China.
What determines these patterns of production?
How do choices end up determining the quantities of
cell phones, automobiles, cellphone service, autorepair service, and the millions of other items that are
produced in the United States and around the world?
How? Goods and services are produced by using pro ductive resources that economists call factors of proFactors of production are grouped into four
categories: duction.
■
■
■
■ Land
Labor
Capital
Entrepreneurship Land The “gifts of nature” that we use to produce
goods and services are called land. In economics,
land is what in everyday language we call natural 0
20
40
60
Percentage of production
Agriculture Manufacturing 80 100 Services The richer the country, the more of its production is services
and the less is food and manufactured goods.
Source of data: CIA Factbook 2008, Central Intelligence Agency. animation resources. It includes land in the everyday sense
together with minerals, oil, gas, coal, water, air,
forests, and fish.
Our land surface and water resources are renewable and some of our mineral resources can be recycled. But the resources that we use to create energy
are nonrenewable—they can be used only once.
Labor The work time and work effort that people
devote to producing goods and services is called
labor. Labor includes the physical and mental efforts
of all the people who work on farms and construction sites and in factories, shops, and offices.
The quality of labor depends on human capital,
which is the knowledge and skill that people obtain
from education, onthejob training, and work experience. You are building your own human capital
right now as you work on your economics course,
and your human capital will continue to grow as you
gain work experience.
Human capital expands over time. Today, 86 percent of the population of the United States have
completed high school and 28 percent have a college
or university degree. Figure 1.2 shows these measures
of the growth of human capital in the United States
over the past century. 9160335_CH01_p001030.qxd 6/22/09 8:55 AM Page 4 CHAPTER 1 What Is Economics? 4 A Measure of Human Capital Percentage of adult population FIGURE 1.2
100 Less than 5 years of
elementary school 75 quantities of goods and services. A small income
leaves a person with few options and small quantities
of goods and services.
People earn their incomes by selling the services of
the factors of production they own:
■ Some high school ■
■ Completed
high school 50 ■ 25 4 years or
more of college
0
1907
Year 1927 1947 1967 1987 2007 Today, 28 percent of the population have 4 years or more of
college, up from 2 percent in 1905. A further 58 percent
have completed high school, up from 10 percent in 1905.
Source of data: U.S. Census Bureau, Statistical Abstract of the
United States. animation Capital The tools, instruments, machines, buildings,
and other constructions that businesses use to produce goods and services are called capital.
In everyday language, we talk about money,
stocks, and bonds as being “capital.” These items are
financial capital. Financial capital plays an important
role in enabling businesses to borrow the funds that
they use to buy physical capital. But because financial
capital is not used to produce goods and services, it is
not a productive resource. The human resource that organizes
labor, land, and capital is called entrepreneurship.
Entrepreneurs come up with new ideas about what
and how to produce, make business decisions, and
bear the risks that arise from these decisions.
Entrepreneurship What determines the quantities of factors of production that are used to produce goods and services?
For Whom? Who consumes the goods and services
that are produced depends on the incomes that people earn. A large income enables a person to buy large Land earns rent.
Labor earns wages.
Capital earns interest.
Entrepreneurship earns profit. Which factor of production earns the most
income? The answer is labor. Wages and fringe benefits are around 70 percent of total income. Land, capital, and entrepreneurship share the rest. These
percentages have been remarkably constant over time.
Knowing how income is shared among the factors
of production doesn’t tell us how it is shared among
individuals. And the distribution of income among
individuals is extremely unequal. You know of some
people who earn very large incomes: Oprah Winfrey
made $260 million in 2007; and Bill Gates’ wealth
increased by $2 billion in 2008.
You know of even more people who earn very
small incomes. Servers at McDonald’s average around
$6.35 an hour; checkout clerks, cleaners, and textile
and leather workers all earn less than $10 an hour.
You probably know about other persistent differences in incomes. Men, on the average, earn more
than women; whites earn more than minorities; college graduates earn more than highschool graduates.
We can get a good sense of who consumes the
goods and services produced by looking at the percentages of total income earned by different groups
of people. The 20 percent of people with the lowest
incomes earn about 5 percent of total income, while
the richest 20 percent earn close to 50 percent of
total income. So on average, people in the richest 20
percent earn more than 10 times the incomes of
those in the poorest 20 percent.
Why is the distribution of income so unequal? Why
do women and minorities earn less than white males?
Economics provides some answers to all these
questions about what, how, and for whom goods and
services are produced and much of the rest of this
book will help you to understand those answers.
We’re now going to look at the second big question of economics: When does the pursuit of selfinterest promote the social interest? This question is a
difficult one both to appreciate and to answer. 9160335_CH01_p001030.qxd 6/22/09 8:55 AM Page 5 Two Big Economic Questions How Can the Pursuit of SelfInterest
Promote the Social Interest?
Every day, you and 304 million other Americans,
along with 6.7 billion people in the rest of the
world, make economic choices that result in what,
how, and for whom goods and services are produced.
SelfInterest A choice is in your selfinterest if you think that choice is the best one available for you.
You make most of your choices in your selfinterest. You use your time and other resources in the
ways that make the most sense to you, and you
don’t think too much about how your choices affect
other people. You order a home delivery pizza
because you’re hungry and want to eat. You don’t
order it thinking that the delivery person needs an
income.
When you act on your selfinterested economic
choices, you come into contact with thousands of
other people who produce and deliver the goods and
services that you decide to buy or who buy the things
that you sell. These people have made their own
choices—what to produce and how to produce it,
whom to hire or to work for, and so on—in their
selfinterest. When the pizza delivery person shows
up at your door, he’s not doing you a favor. He’s earning his income and hoping for a good tip.
Social Interest Selfinterested choices promote the
social interest if they lead to an outcome that is the
best for society as a whole—an outcome that uses
resources efficiently and distributes goods and services equitably (or fairly) among individuals.
Resources are used efficiently when goods and
services are produced 1. At the lowest possible cost, and
2. In the quantities that give the greatest possible
benefit.
The Big Question How can we organize our eco nomic lives so that when each one of us makes
choices that are in our selfinterest, it turns out that
these choices also promote the social interest? Does
voluntary trading in free markets achieve the social
interest? Do we need government action to guide our
choices to achieve the social interest? Do we need
international cooperation and treaties to achieve the
global social interest?
Let’s put flesh on these broad questions with some
examples. 5 SelfInterest and the Social Interest
To get started thinking about the tension between
selfinterest and the social interest, we’ll consider five
topics that generate discussion in today’s world. Here,
we will briefly introduce the topics and identify some
of the economic questions that they pose. We’ll
return to each one of them as you learn more of the
economic ideas and tools that can be used to understand these issues. The topics are
■ Globalization
■ The informationage economy
■ Global warming
■ Natural resource depletion
■ Economic instability
Globalization The term globalization means the
expansion of international trade, borrowing and lending, and investment.
Whose selfinterest does globalization serve? Is it
only in the selfinterest of the multinational firms that
produce in lowcost regions and sell in highprice
regions? Is globalization in the interest of consumers
who buy lowercost goods? Is globalization in the
interest of the worker in Malaysia who sews your new
running shoes? Is globalization in your selfinterest and
in the social interest? Or should we limit globalization
and restrict imports of cheap foreignproduced goods
and services? Globalization Today
Life in a Small and Ever Shrinking World
Every day, 40,000 people travel by air between the
United States and Asia and Europe. A phone call or a
videoconference with people who live 10,000 miles
apart is a common and easily affordable event.
When Nike produces sports shoes, people in
China, Indonesia, or Malaysia get work. When Apple
designs a new generation iPod, electronics factories in
China, Japan, Korea, and Taiwan produce and assemble the parts. When Nintendo creates a new game for
the Wii, programmers in India write the code. And
when China Airlines buys new airplanes, Americans
who work at Boeing build them.
While globalization brings expanded production
and job opportunities for Asian workers, it destroys
many American jobs. Workers across the manufacturing industries must learn new skills, or take lowerpaid service jobs, or retire earlier than planned. 9160335_CH01_p001030.qxd 6 6/22/09 8:55 AM Page 6 CHAPTER 1 What Is Economics? The InformationAge Economy The technological
change of the 1990s and 2000s has been called the
Information Revolution.
During the information revolution were scarce
resources used in the best possible way? Who benefitted from Bill Gates’ decision to quit Harvard and create Microsoft? Did Microsoft produce operating
systems for the personal computer that served the
social interest? Did it sell its programs for prices that
served the social interest? Did Bill Gates have to be
paid what has now grown to $55 billion to produce
the successive generations of Windows, Microsoft
Office, and other programs? Did Intel make the right
quality of chips and sell them in the right quantities
for the right prices? Or was the quality too low and
the price too high? Would the social interest have
been better served if Microsoft and Intel had faced
competition from other firms? Global Warming Global warming and its effect on The Source of the InformationAge A Hotter Planet So Much from One Tiny Chip Melting Ice and the Changing Climate The microprocessor or computer chip created the
information age. Gordon Moore of Intel predicted in
1965 that the number of transistors that could be
placed on one chip would double every 18 months
(Moore’s law). This prediction turned out to be
remarkably accurate. In 1980, an Intel chip had
60,000 transistors. In 2008, Intel’s Core 2 Duo
processor that you might be using on your personal
computer has 291 million transistors.
The spinoffs from faster and cheaper computing
were widespread. Telecommunications became clearer
and faster; music and movie recording became more
realistic; routine tasks that previously required human
decision and action were automated.
All the new products and processes, and the lowcost computing power that made them possible, were
produced by people who made choices in their own
selfinterest. They did not result from any grand
design or government economic plan.
When Gordon Moore set up Intel and started
making chips, no one had told him to do so, and he
wasn’t thinking how much easier it would be for you
to turn in your essay on time if you had a faster laptop. When Bill Gates quit Harvard to set up
Microsoft, he wasn’t thinking about making it easier
to use a computer. Moore, Gates, and thousands of
other entrepreneurs were in hot pursuit of the big
prizes that many of them succeeded in winning. Retreating polar icecaps are a vivid illustration of a
warming planet. Over the past 100 years, the Earth’s
surface air temperature is estimated to have risen by
about three quarters of a degree Celsius. Uncertainty
surrounds the causes, likely future amount, and
effects of this temperature increase.
The consensus is that the temperature is rising
because the amount of carbon dioxide in the Earth’s
atmosphere is increasing, and that human economic
activity is a source of the increased carbon concentration.
Forests convert carbon dioxide to oxygen and so
act as carbon sinks, but they are shrinking.
Two thirds of the world’s carbon emissions come
from the United States, China, the European Union,
Russia, and India. The fastest growing emissions are
coming from India and China.
Burning fossil fuels—coal and oil—to generate
electricity and to power airplanes, automobiles, and
trucks pours a staggering 28 billions tons—4 tons per
person—of carbon dioxide into the atmosphere each
year.
The amount of future global warming and its
effects are uncertain. If the temperature rise continues, the Earth’s climate will change, ocean levels will
rise, and lowlying coastal areas will need to be protected against the rising tides by expensive barriers. climate change is a huge political issue today. Every
serious political leader is acutely aware of the problem and of the popularity of having proposals that
might lower carbon emissions.
Every day, when you make selfinterested choices
to use electricity and gasoline, you contribute to carbon emissions; you leave your carbon footprint. You
can lessen your carbon footprint by walking, riding a
bike, taking a cold shower, or planting a tree.
But can each one of us be relied upon to make
decisions that affect the Earth’s carbondioxide concentration in the social interest? Must governments
change the incentives we face so that our selfinterested choices advance the social interest? How can
governments change incentives? How can we encourage the use of wind and solar power to replace the
burning of fossil fuels that bring climate change? 9160335_CH01_p001030.qxd 6/22/09 8:55 AM Page 7 Two Big Economic Questions Natural Resource Depletion Tropical rainforests and ocean fish stocks are disappearing quickly. No one
owns these resources and everyone is free to take what
they want. When Japanese, Spanish, and Russian
trawlers scoop up fish in international waters, no one
keeps track of the quantities of fish they catch and no
one makes them pay. The fish are free.
Each one of us makes selfinterested economic
choices to buy products that destroy natural resources
and kill wild fish stocks. When you buy soap or
shampoo or eat fish and contribute to the depletion
of natural resources, are your selfinterested choices
damaging the social interest? If they are, what can be
done to change your choices so that they serve the
social interest?
Economic Instability The past 20 years have been ones of remarkable economic stability, so much so
that they’ve been called the Great Moderation. Even
the economic shockwaves of 9/11 brought only a
small dip in the strong pace of U.S. and global eco Running Out of Natural Resources
Disappearing Forests and Fish
Tropical rainforests in South America, Africa, and Asia
support the lives of 30 million species of plants, animals, and insects—approaching 50 percent of all the
species on the planet. These rainforests provide us
with the ingredients for many goods, including soaps,
mouthwashes, shampoos, food preservatives, rubber,
nuts, and fruits. The Amazon rainforest alone converts about 1 trillion pounds of carbon dioxide into
oxygen each year.
Yet tropical rainforests cover less than 2 percent
of the earth’s surface and are heading for extinction.
Logging, cattle ranching, mining, oil extraction,
hydroelectric dams, and subsistence farming destroy
an area the size of two football fields every second, or
an area larger than New York City every day. At the
current rate of destruction, almost all the tropical
rainforest ecosystems will be gone by 2030.
What is happening to the tropical rainforests is
also happening to ocean fish stocks. Overfishing has
almost eliminated cod from the Atlantic Ocean and
the southern bluefin tuna from the South Pacific
Ocean. Many other species of fish are on the edge of
extinction in the wild and are now available only
from fish farms. 7 nomic expansion. But in August 2007, a period of
financial stress began.
Banks’ choices to lend and people’s choices to borrow were made in selfinterest. But did this lending and
borrowing serve the social interest? Did the Fed’s bail
out of troubled banks serve the social interest? Or
might the Fed’s rescue action encourage banks to repeat
their dangerous lending in the future? The End of the Great Moderation
A Credit Crunch
Flush with funds, and offering record low interest
rates, banks went on a lending spree to home buyers.
Rapidly rising home prices made home owners feel
well off and they were happy to borrow and spend.
Home loans were bundled into securities that were
sold and resold to banks around the world.
In 2006, interest rates began to rise, the rate of
rise in home prices slowed, and borrowers defaulted
on their loans. What started as a trickle became a
flood. By mid2007, banks took losses that totaled
billions of dollars as more people defaulted.
Global credit markets stopped working, and people began to fear a prolonged slowdown in economic
activity. Some even feared the return of the economic
trauma of the Great Depression of the 1930s when
more than 20 percent of the U.S. labor force was
unemployed. The Federal Reserve, determined to
avoid a catastrophe, started lending on a very large
scale to the troubled banks. Review Quiz ◆
1
2 Describe the broad facts about what, how, and
for whom goods and services are produced.
Use headlines from the recent news to illustrate
the potential for conflict between selfinterest
and the social interest.
Work Study Plan 1.2
and get instant feedback. We’ve looked at five topics that illustrate the big
question: How can choices made in the pursuit of
selfinterest also promote the social interest? While
working through this book, you will encounter the
principles that help economists figure out when the
social interest is being served, when it is not, and
what might be done when the social interest is not
being served? 9160335_CH01_p001030.qxd 8 6/22/09 8:55 AM Page 8 CHAPTER 1 What Is Economics? ◆ The Economic Way
of Thinking
The questions that economics tries to answer tell us
about the scope of economics. But they don’t tell us
how economists think about these questions and go
about seeking answers to them.
You’re now going to begin to see how economists
approach economic questions. We’ll look at the
ideas that define the economic way of thinking. This
way of thinking needs practice, but it is powerful,
and as you become more familiar with it, you’ll
begin to see the world around you with a new and
sharper focus. Choices and Tradeoffs
Because we face scarcity, we must make choices.
And when we make a choice, we select from the
available alternatives. For example, you can spend
Saturday night studying for your next economics
test and having fun with your friends, but you
can’t do both of these activities at the same time.
You must choose how much time to devote to
each. Whatever choice you make, you could have
chosen something else.
You can think about your choice as a tradeoff. A
tradeoff is an exchange—giving up one thing to get
something else. When you choose how to spend your
Saturday night, you face a tradeoff between studying
and hanging out with your friends.
Guns Versus Butter The classic tradeoff is between
guns and butter. “Guns” and “butter” stand for any
pair of goods. They might actually be guns and butter. Or they might be broader categories such as
national defense and food. Or they might be any pair
of specific goods or services such as cola and pizza,
baseball bats and tennis rackets, colleges and hospitals, realtor services and career counseling.
Regardless of the specific objects that guns and
butter represent, the gunsversusbutter tradeoff captures a hard fact of life: If we want more of one thing,
we must give up something else to get it. To get more
“guns” we must give up some “butter.”
The idea of a tradeoff is central to economics.
We’ll look at some examples, beginning with the big
questions: What, How, and For Whom goods and
services are produced? We can view each of these
questions in terms of tradeoffs. What, How, and For Whom Tradeoffs
The questions what, how, and for whom goods and
services are produced all involve tradeoffs that are
similar to that between guns and butter.
What Tradeoffs What goods and services are pro duced depends on choices made by each one of us, by
our government, and by the businesses that produce
the things we buy. Each of these choices involves a
tradeoff.
Each one of us faces a tradeoff when we choose
how to spend our income. You go to the movies this
week, but you forgo a few cups of coffee to buy the
ticket. You trade off coffee for a movie.
The federal government faces a tradeoff when it
chooses how to spend our tax dollars. Congress votes
for more national defense but cuts back on educational programs. Congress trades off education for
national defense.
Businesses face a tradeoff when they decide what
to produce. Nike hires Tiger Woods and allocates
resources to designing and marketing a new golf ball
but cuts back on its development of a new running
shoe. Nike trades off running shoes for golf balls.
How Tradeoffs How businesses produce the goods and services we buy depends on their choices. These
choices involve tradeoffs. For example, when Krispy
Kreme opens a new store with an automated production line and closes one with a traditional kitchen, it
trades off labor for capital. When American Airlines
replaces checkin agents with self checkin kiosks, it
also trades off labor for capital.
For Whom Tradeoffs For whom goods and services
are produced depends on the distribution of buying
power. Buying power can be redistributed—transferred from one person to another—in three ways:
by voluntary payments, by theft, or through taxes
and benefits organized by government. Redistribution brings tradeoffs.
Each of us faces a tradeoff when we choose how
much to contribute to the United Nations’ famine
relief fund. You donate $50 and cut your spending.
You trade off your own spending for a small increase
in economic equality. We also face a tradeoff when
we vote to increase the resources for catching thieves
and enforcing the law. We trade off goods and services for an increase in the security of our property. 9160335_CH01_p001030.qxd 6/22/09 8:55 AM Page 9 T he Economic Way of Thinking We also face a for whom tradeoff when we vote for
taxes and social programs that redistribute buying
power from the rich to the poor. These redistribution
programs confront society with what has been called
the big tradeoff—the tradeoff between equality and
efficiency. Taxing the rich and making transfers to the
poor bring greater economic equality. But taxing productive activities such as running a business, working
hard, and developing a more productive technology
discourages these activities. So taxing productive
activities means producing less. A more equal distribution means there is less to share.
Think of the problem of how to share a pie that
everyone contributes to baking. If each person receives
a share of the pie that is proportional to her or his
effort, everyone will work hard and the pie will be as
large as possible. But if the pie is shared equally,
regardless of contribution, some talented bakers will
slack off and the pie will shrink. The big tradeoff is
one between the size of the pie and how equally it is
shared. We trade off some pie for increased equality. Choices Bring Change
What, how, and for whom goods and services are produced changes over time. The quantity and range of
goods and services available today is much greater than
it was a generation ago. But the quality of economic
life (and its rate of improvement) doesn’t depend
purely on nature and on luck. It depends on many of
the choices made by each one of us, by governments,
and by businesses. These choices also involve tradeoffs.
One choice is that of how much of our income to
consume and how much to save. Our saving can be
channeled through the financial system to finance
businesses and to pay for new capital that increases
production. The more we save, the more financial capital is available for businesses to use to buy physical
capital, so the more goods and services we can produce
in the future. When you decide to save an extra $1,000
and forgo a vacation, you trade off the vacation for a
higher future income. If everyone saves an extra
$1,000 and businesses buy more equipment that
increases production, future consumption per person
rises. As a society, we trade off current consumption
for economic growth and higher future consumption.
A second choice is how much effort to devote to
education and training. By becoming better educated
and more highly skilled, we become more productive
and are able to produce more goods and services. 9 When you decide to remain in school for another
two years to complete a professional degree and forgo
a huge chunk of leisure time, you trade off leisure
today for a higher future income. If everyone
becomes better educated, production increases and
income per person rises. As a society, we trade off
current consumption and leisure time for economic
growth and higher future consumption.
A third choice is how much effort to devote to
research and the development of new products and
production methods. Ford Motor Company can hire
people either to design a new robotic assembly line or
to operate the existing plant and produce cars. The
robotic plant brings greater productivity in the future
but means smaller current production—a tradeoff of
current production for greater future production.
Seeing choices as tradeoffs emphasizes the idea
that to get something, we must give up something.
What we give up is the cost of what we get.
Economists call this cost the opportunity cost. Opportunity Cost
“There’s no such thing as a free lunch” expresses the
central idea of economics: Every choice has a cost.
The opportunity cost of something is the highestvalued alternative that we must give up to get it.
For example, you face an opportunity cost of being
in school. That opportunity cost is the highestvalued
alternative that you would do if you were not in
school. If you quit school and take a job at
McDonald’s, you earn enough to go to ball games and
movies and spend lots of free time with your friends. If
you remain in school, you can’t afford these things.
You will be able to buy these things when you graduate
and get a job, and that is one of the payoffs from being
in school. But for now, when you’ve bought your
books, you have nothing left for games and movies.
Working on assignments leaves even less time for
hanging out with your friends. Giving up games,
movies, and free time is part of the opportunity cost of
being in school.
All the what, how, and for whom tradeoffs involve
opportunity cost. The opportunity cost of some guns
is the butter forgone; the opportunity cost of a movie
ticket is the number of cups of coffee forgone.
And the choices that bring change also involve
opportunity cost. The opportunity cost of more
goods and services in the future is less consumption
today. 9160335_CH01_p001030.qxd 10 6/22/09 8:55 AM Page 10 CHAPTER 1 What Is Economics? Choosing at the Margin
You can allocate the next hour between studying and
instant messaging your friends. But the choice is not
all or nothing. You must decide how many minutes to
allocate to each activity. To make this decision, you
compare the benefit of a little bit more study time with
its cost—you make your choice at the margin.
The benefit that arises from an increase in an
activity is called marginal benefit. For example, suppose that you’re spending four nights a week studying
and your grade point average (GPA) is 3.0. You
decide that you want a higher GPA and decide to
study an extra night each week. Your GPA rises to
3.5. The marginal benefit from studying for one extra
night a week is the 0.5 increase in your GPA. It is not
the 3.5. You already have a 3.0 from studying for four
nights a week, so we don’t count this benefit as resulting from the decision you are now making.
The cost of an increase in an activity is called
marginal cost. For you, the marginal cost of increasing
your study time by one night a week is the cost of the
additional night not spent with your friends (if that is
your best alternative use of the time). It does not
include the cost of the four nights you are already
studying.
To make your decision, you compare the marginal
benefit from an extra night of studying with its marginal cost. If the marginal benefit exceeds the marginal
cost, you study the extra night. If the marginal cost
exceeds the marginal benefit, you do not study the
extra night.
By evaluating marginal benefits and marginal costs
and choosing only those actions that bring greater
benefit than cost, we use our scarce resources in the
way that makes us as well off as possible. The central idea of economics is that we can predict how choices will change by looking at changes in
incentives. More of an activity is undertaken when its
marginal cost falls or its marginal benefit rises; less of
an activity is undertaken when its marginal cost rises
or its marginal benefit falls.
Incentives are also the key to reconciling selfinterest and social interest. When our choices are not
in the social interest, it is because of the incentives
we face. One of the challenges for economists is to
figure out the incentive systems that result in selfinterested choices also being in the social interest. Human Nature, Incentives, and Institutions
Economists take human nature as given and view
people as acting in their selfinterest. All people—
consumers, producers, politicians, and public servants—pursue their selfinterest.
Selfinterested actions are not necessarily selfish
actions. You might decide to use your resources in
ways that bring pleasure to others as well as to yourself. But a selfinterested act gets the most value for
you based on your view about value.
If human nature is given and if people act in their
selfinterest, how can we take care of the social interest? Economists answer this question by emphasizing
the crucial role that institutions play in influencing
the incentives that people face as they pursue their
selfinterest.
A system of laws that protect private property
and markets that enable voluntary exchange are the
fundamental institutions. You will learn as you
progress with your study of economics that where
these institutions exist, selfinterest can indeed promote the social interest. Responding to Incentives
When we make choices we respond to incentives. A
change in marginal cost or a change in marginal
benefit changes the incentives that we face and leads
us to change our choice.
For example, suppose your economics instructor
gives you a set of problems and tells you that all the
problems will be on the next test. The marginal benefit from working these problems is large, so you diligently work them all. In contrast, if your math
instructor gives you a set of problems and tells you
that none of the problems will be on the next test,
the marginal benefit from working these problems is
lower, so you skip most of them. Review Quiz ◆
1
2
3
4 Provide three everyday examples of tradeoffs and
describe the opportunity cost involved in each.
Provide three everyday examples to illustrate
what we mean by choosing at the margin.
How do economists predict changes in choices?
What do economists say about the role of institutions in promoting the social interest?
Work Study Plan 1.3
and get instant feedback. 9160335_CH01_p001030.qxd 6/22/09 8:55 AM Page 11 E conomics as Social Science and Policy Tool ◆ Economics as Social Science and
Policy Tool
Economics is both a science and a set of tools that
can be used to make policy decisions. Economics as Social Science
As social scientists, economists seek to discover how
the economic world works. In pursuit of this goal,
like all scientists, they distinguish between two types
of statements: positive and normative.
Positive Statements Positive statements are about
what is. They say what is currently believed about
the way the world operates. A positive statement
might be right or wrong, but we can test a positive
statement by checking it against the facts. “Our
planet is warming because of the amount of coal
that we’re burning” is a positive statement. “A rise
in the minimum wage will bring more teenage
unemployment” is another positive statement. Each
statement might be right or wrong, and it can be
tested.
A central task of economists is to test positive
statements about how the economic world works
and to weed out those that are wrong. Economics
first got off the ground in the late 1700s, so economics is a young subject compared with, for example, math and physics, and much remains to be
discovered.
Normative Statements Normative statements are
statements about what ought to be. These statements
depend on values and cannot be tested. The statement “We ought to cut back on our use of coal” is a
normative statement. “The minimum wage should
not be increased” is another normative statement.
You may agree or disagree with either of these statements, but you can’t test them. They express an opinion, but they don’t assert a fact that can be checked.
They are not economics.
Unscrambling Cause and Effect Economists are espe cially interested in positive statements about cause
and effect. Are computers getting cheaper because
people are buying them in greater quantities? Or are
people buying computers in greater quantities
because they are getting cheaper? Or is some third
factor causing both the price of a computer to fall
and the quantity of computers to increase? 11 To answer questions such as these, economists
create and test economic models. An economic model
is a description of some aspect of the economic
world that includes only those features that are
needed for the purpose at hand. For example, an
economic model of a cellphone network might
include features such as the prices of calls, the number of cellphone users, and the volume of calls. But
the model would ignore such details as cellphone
colors and ringtones.
A model is tested by comparing its predictions with
the facts. But testing an economic model is difficult
because we observe the outcomes of the simultaneous
operation of many factors. To cope with this problem, economists use natural experiments, statistical
investigations, and economic experiments.
Natural Experiment A natural experiment is a situa tion that arises in the ordinary course of economic
life in which the one factor of interest is different and
other things are equal (or similar). For example,
Canada has higher unemployment benefits than the
United States, but the people in the two nations are
similar. So to study the effect of unemployment benefits on the unemployment rate, economists might
compare the United States with Canada.
Statistical Investigation A statistical investigation looks for correlation—a tendency for the values of
two variables to move together (either in the same
direction or in opposite directions) in a predictable
and related way. For example, cigarette smoking and
lung cancer are correlated. Sometimes a correlation
shows a causal influence of one variable on the
other. For example, smoking causes lung cancer. But
sometimes the direction of causation is hard to
determine.
Steven Levitt, the author of Freakonomics, whom
you can meet on pp. 224–226, is a master in the use
of a combination of the natural experiment and statistical investigation to unscramble cause and effect.
He has used the tools of economics to investigate the
effects of good parenting on education (not very
strong), to explain why drug dealers live with their
mothers (because they don’t earn enough to live independently), and (controversially) the effects of abortion law on crime.
Economic Experiment An economic experiment puts people in a decisionmaking situation and varies the
influence of one factor at a time to discover how they
respond. 9160335_CH01_p001030.qxd 12 6/22/09 8:55 AM Page 12 CHAPTER 1 What Is Economics? Economics as Policy Tool
Economics is useful. It is a toolkit for making decisions. And you don’t need to be a fullyfledged
economist to think like one and to use the insights
of economics as a policy tool.
Economics provides a way of approaching problems in all aspects of our lives. Here, we’ll focus on
the three broad areas of:
■
■
■ Personal economic policy
Business economic policy
Government economic policy Personal Economic Policy Should you take out a
student loan? Should you get a weekend job? Should
you buy a used car or a new one? Should you rent an
apartment or take out a loan and buy a condominium? Should you pay off your credit card balance
or make just the minimum payment? How should
you allocate your time between study, working for a
wage, caring for family members, and having fun?
How should you allocate your time between studying
economics and your other subjects? Should you quit
school after getting a bachelor’s degree or should you
go for a master’s or a professional qualification?
All these questions involve a marginal benefit and
a marginal cost. And although some of the numbers
might be hard to pin down, you will make more solid
decisions if you approach these questions with the
tools of economics.
Business Economic Policy Should Sony make only
flat panel televisions and stop making conventional
ones? Should Texaco get more oil and gas from the
Gulf of Mexico or from Alaska? Should Palm outsource its online customer services to India or run the
operation from California? Should Marvel Studios
produce SpiderMan 4, a sequel to SpiderMan 3?
Can Microsoft compete with Google in the search
engine business? Can eBay compete with the surge of
new Internet auction services? Is Jason Giambi really
worth $23,400,000 to the New York Yankees?
Like personal economic questions, these business
questions involve the evaluation of a marginal benefit
and a marginal cost. Some of the questions require a
broader investigation of the interactions of individuals
and firms. But again, by approaching these questions
with the tools of economics and by hiring economists
as advisers, businesses can make better decisions. Government Economic Policy How can California balance its budget? Should the federal government
cut taxes or raise them? How can the tax system be
simplified? Should people be permitted to invest
their Social Security money in stocks that they pick
themselves? Should Medicaid and Medicare be
extended to the entire population? Should there be
a special tax to penalize corporations that send jobs
overseas? Should cheap foreign imports of furniture
and textiles be limited? Should the farms that grow
tomatoes and sugar beets receive a subsidy? Should
water be transported from Washington and Oregon
to California?
These government policy questions call for decisions that involve the evaluation of a marginal benefit
and a marginal cost and an investigation of the interactions of individuals and businesses. Yet again, by
approaching these questions with the tools of economics, governments make better decisions.
Notice that all the policy questions we’ve just
posed involve a blend of the positive and the normative. Economics can’t help with the normative part—
the objective. But for a given objective, economics
provides a method of evaluating alternative solutions.
That method is to evaluate the marginal benefits and
marginal costs and to find the solution that brings
the greatest available gain. Review Quiz ◆
1 2 3
4
5 What is the distinction between a positive statement and a normative statement? Provide an
example (different from those in the chapter) of
each type of statement.
What is a model? Can you think of a model
that you might use (probably without thinking
of it as a model) in your everyday life?
What are the three ways in which economists
try to disentangle cause and effect?
How is economics used as a policy tool?
What is the role of marginal analysis in the use
of economics as a policy tool?
Work Study Plan 1.4
and get instant feedback. 9160335_CH01_p001030.qxd 6/22/09 8:55 AM Page 13 Summary SUMMARY ◆ Key Points ■ Definition of Economics (p. 2) ■ ■ ■ ■ All economic questions arise from scarcity—from
the fact that wants exceed the resources available
to satisfy them.
Economics is the social science that studies the
choices that people make as they cope with
scarcity.
The subject divides into microeconomics and
macroeconomics. Two Big Economic Questions (pp. 3–7)
■ ■ ■ ■ ■ Two big questions summarize the scope of
economics:
1. How do choices end up determining what,
how, and for whom goods and services are produced?
2. When do choices made in the pursuit of selfinterest also promote the social interest? The classic gunsversusbutter tradeoff represents
all tradeoffs.
All economic questions involve tradeoffs.
The big social tradeoff is that between equality
and efficiency.
The highestvalued alternative forgone is the
opportunity cost of what is chosen.
Choices are made at the margin and respond to
incentives. Economics as Social Science and
Policy Tool (pp. 11–12) ■ ■ ■ The Economic Way of Thinking (pp. 8–10)
■ 13 Economists distinguish between positive statements—what is—and normative statements—
what ought to be.
To explain the economic world, economists create
and test economic models.
Economics is used in personal, business, and government economic policy decisions.
The main policy tool is the evaluation and comparison of marginal cost and marginal benefit. Every choice is a tradeoff—exchanging more of
something for less of something else. Key Terms
Big tradeoff, 9
Capital, 4
Economic model, 11
Economics, 2
Entrepreneurship, 4
Factors of production, 3
Goods and services, 3
Human capital, 3
Incentive, 2 Interest, 4
Labor, 3
Land, 3
Macroeconomics, 2
Margin, 10
Marginal benefit, 10
Marginal cost, 10
Microeconomics, 2
Opportunity cost, 9 Profit, 4
Rent, 4
Scarcity, 2
Selfinterest, 5
Social interest, 5
Tradeoff, 8
Wages, 4 9160335_CH01_p001030.qxd 14 6/22/09 8:55 AM Page 14 CHAPTER 1 What Is Economics? PROBLEMS and APPLICATIONS ◆ Work problems 1–6 in Chapter 1 Study Plan and get instant feedback.
Work problems 7–12 as Homework, a Quiz, or a Test if assigned by your instructor. 1. Apple Computer Inc. decides to make iTunes
freely available in unlimited quantities.
a. How does Apple’s decision change the opportunity cost of a download?
b. Does Apple’s decision change the incentives
that people face?
c. Is Apple’s decision an example of a microeconomic or a macroeconomic issue?
2. Which of the following pairs does not match:
a. Labor and wages?
b. Land and rent?
c. Entrepreneurship and profit?
d. Capital and profit?
3. Explain how the following news headlines concern selfinterest and the social interest:
a. WalMart Expands in Europe
b. McDonald’s Moves into Salads
c. Food Must Be Labeled with Nutrition
Information
4. The night before an economics test, you decide
to go to the movies instead of staying home and
working your MyEconLab Study Plan. You get
50 percent on your test compared with the 70
percent that you normally score.
a. Did you face a tradeoff?
b. What was the opportunity cost of your
evening at the movies?
5. Which of the following statements is positive,
which is normative, and which can be tested?
a. The U.S. government should cut its imports.
b. China is the United States’ largest trading
partner.
c. If the price of antiretroviral drugs increases,
HIV/AIDS sufferers will decrease their consumption of the drugs.
6. As London prepares to host the 2012 Olympic
Games, concern about the cost of the event
increases. An example:
Costs Soar for London Olympics
The regeneration of East London is set to add
extra £1.5 billion to taxpayers’ bill.
The Times, London, July 6, 2006
Is the cost of regenerating East London an
opportunity cost of hosting the 2012 Olympic
Games? Explain why or why not. 7. Before starring as Tony Stark in Iron Man,
Robert Downey Jr. had played in 45 movies that
had average firstweekend box office revenues of
a bit less than $5 million. Iron Man grossed $102
million on its opening weekend.
a. How do you expect the success of Iron Man to
influence the opportunity cost of hiring
Robert Downey Jr.?
b. How have the incentives for a movie producer
to hire Robert Downey Jr. changed?
8. How would you classify a movie star as a factor
of production?
9. How does the creation of a successful movie
influence what, how, and for whom goods and
services are produced?
10. How does the creation of a successful movie
illustrate selfinterested choices that are also in
the social interest?
11. Look at today’s Wall Street Journal.
a. What is the top economic news story?
With which of the big questions does it deal?
(It must deal with at least one of them and
might deal with more than one.)
b. What tradeoffs does the news item discuss or
imply?
c. Write a brief summary of the news item using
the economic vocabulary that you have
learned in this chapter and as many as possible
of the key terms listed on p. 13.
12. Use the link in MyEconLab (Textbook
Resources, Chapter 1) to visit Resources for
Economists on the Internet. This Web site is a
good place from which to search for economic
information on the Internet.
Click on “Blogs, Commentaries, and Podcasts,”
and then click on the BeckerPosner Blog.
a. Read the latest blog by these two outstanding
economists.
b. As you read this blog, think about what it is
saying about the “what,” “how,” and “for
whom” questions.
c. As you read this blog, think about what it is saying about selfinterest and the social interest. 9160335_CH01_p001030.qxd 6/22/09 8:55 AM Page 15 A ppendix: Graphs in Economics After studying this appendix,
you will be able to:
Make and interpret a timeseries graph, a crosssection
graph, and a scatter diagram
Distinguish between linear and nonlinear relationships
and between relationships that have a maximum and a
minimum ■ –60 Graph relationships among more than two variables 20 B C
32ºF and
20,320 ft 15
10 32ºF and
0 ft –30 A
0 30 –5
Negative x 60
90
120
Temperature (degrees F)
Positive –10 Graphs have axes that measure quantities as distances.
Here, the horizontal axis (xaxis) measures temperature, and
the vertical axis (yaxis) measures height. Point A represents
a fishing boat at sea level (0 on the yaxis) on a day when
the temperature is 32ºF. Point B represents a climber at the
top of Mt. McKinley, 20,320 feet above sea level at a
temperature of 0ºF. Point C represents a climber at the top
of Mt. McKinley, 20,320 feet above sea level at a temperature of 32ºF. ◆ Graphing Data
A graph represents a quantity as a distance on a line.
In Fig. A1.1, a distance on the horizontal line represents temperature, measured in degrees Fahrenheit. A
movement from left to right shows an increase in
temperature. The point 0 represents zero degrees
Fahrenheit. To the right of 0, the temperature is positive. To the left of 0 (as indicated by the minus sign),
the temperature is negative. A distance on the vertical
line represents height, measured in thousands of feet.
The point 0 represents sea level. Points above 0 represent feet above sea level. Points below 0 (indicated by
a minus sign) represent feet below sea level.
By setting two scales perpendicular to each other,
as in Fig. A1.1, we can visualize the relationship
between two variables. The scale lines are called axes.
The vertical line is the yaxis, and the horizontal line
is the xaxis. Each axis has a zero point, which is
shared by the two axes and called the origin.
We need two bits of information to make a twovariable graph: the value of the x variable and the
value of the y variable. For example, off the coast of
Alaska, the temperature is 32 degrees—the value of x.
A fishing boat is located at 0 feet above sea level—the
value of y. These two bits of information appear as
point A in Fig. A1.1. A climber at the top of Mount
McKinley on a cold day is 20,320 feet above sea level
in a zerodegree gale. These two pieces of information
appear as point B. On a warmer day, a climber might 0ºF and
20,320 ft 25 5 Define and calculate the slope of a line ■ y Origin Below sea level ■ Height (thousands of feet) Above sea level Graphs in Economics ■ Making a Graph FIGURE A1.1 APPENDIX 15 animation be at the peak of Mt. McKinley when the temperature
is 32 degrees, at point C.
We can draw two lines, called coordinates, from
point C. One, called the ycoordinate, runs from C to
the horizontal axis. Its length is the same as the value
marked off on the yaxis. The other, called the xcoordinate, runs from C to the vertical axis. Its length
is the same as the value marked off on the xaxis. We
describe a point on a graph by the values of its xcoordinate and its ycoordinate.
Graphs like that in Fig. A1.1 can show any type
of quantitative data on two variables. Economists use
three types of graphs based on the principles in Fig.
A1.1 to reveal and describe the relationships among
variables. They are
■
■
■ Timeseries graphs
Crosssection graphs
Scatter diagrams 9160335_CH01_p001030.qxd 6/22/09 8:55 AM Page 16 CHAPTER 1 What Is Econom ics? 16 TimeSeries Graphs
Price of gasoline (2006 dollars per gallon) A timeseries graph measures time (for example,
months or years) on the xaxis and the variable or
variables in which we are interested on the yaxis.
Figure A1.2 is an example of a timeseries graph. It
provides some information about the price of gasoline. In this figure, we measure time in years starting
in 1973. We measure the price of gasoline (the variable that we are interested in) on the yaxis.
The point of a timeseries graph is to enable us
to visualize how a variable has changed over time and
how its value in one period relates to its value in
another period.
A timeseries graph conveys an enormous
amount of information quickly and easily, as this
example illustrates. It shows FIGURE A1.2 A TimeSeries Graph 3.00
High
2.50
Rising
quickly
2.00 Falling
quickly Rising
slowly 1.50
Falling
slowly Low 1.00
1973 1978 1983 1988 1993 1998 2003 2008 Year
■ ■ ■ The level of the price of gasoline—when it is high
and low. When the line is a long way from the
xaxis, the price is high, as it was, for example, in
1981. When the line is close to the xaxis, the
price is low, as it was, for example, in 1998.
How the price changes—whether it rises or falls.
When the line slopes upward, as in 1979, the price
is rising. When the line slopes downward, as in
1986, the price is falling.
The speed with which the price changes—whether
it rises or falls quickly or slowly. If the line is very
steep, then the price rises or falls quickly. If the
line is not steep, the price rises or falls slowly. For
example, the price rose quickly between 1978 and
1980 and slowly between 1994 and 1996. The
price fell quickly between 1985 and 1986 and
slowly between 1990 and 1994. A timeseries graph also reveals whether there is a
general tendency for a variable to move in
one direction. A trend might be upward or downward. In Fig. A1.2, the price of gasoline had a general
tendency to fall during the 1980s and 1990s. That is,
although the price rose and fell, the general tendency
was for it to fall—the price had a downward trend.
During the 2000s, the trend has been upward.
A timeseries graph also helps us to detect fluctuations in a variable around its trend. You can see
some peaks and troughs in the price of gasoline in
Fig. A1.2.
Finally, a timeseries graph also lets us quickly
compare the variable in different periods. Figure A1.2
shows that the 1970s and 1980s were different from trend—a A timeseries graph plots the level of a variable on the
yaxis against time (day, week, month, or year) on the xaxis. This graph shows the price of gasoline (in 2006 dollars per gallon) each year from 1973 to 2006. It shows us
when the price of gasoline was high and when it was low,
when the price increased and when it decreased, and when
the price changed quickly and when it changed slowly.
animation the 1990s. The price of gasoline fluctuated more during the 1970s and 1980s than it did in the 1990s.
You can see that a timeseries graph conveys a
wealth of information, and it does so in much less
space than we have used to describe only some of its
features. But you do have to “read” the graph to
obtain all this information. CrossSection Graphs
A crosssection graph shows the values of an economic
variable for different groups or categories at a point
in time. Figure A1.3, called a bar chart, is an example
of a crosssection graph.
The bar chart in Fig. A1.3 shows 10 leisure pursuits and the percentage of the U. S. population that
participated in them during 2005. The length of each
bar indicates the percentage of the population. This
figure enables you to compare the popularity of these
10 activities. And you can do so much more quickly
and clearly than by looking at a list of numbers. 9160335_CH01_p001030.qxd 6/22/09 8:55 AM Page 17 Appendix: Graphs in Economics A CrossSection Graph FIGURE A1.3 Scatter Diagrams
A scatter diagram plots the value of one variable against
the value of another variable. Such a graph reveals
whether a relationship exists between two variables
and describes their relationship. Figure A1.4(a) shows
the relationship between expenditure and income.
Each point shows expenditure per person and income
per person in a given year from 1997 to 2007. The
points are “scattered” within the graph. The point
labeled A tells us that in 2000, income per person was
$25,472 and expenditure per person was $23,862.
The dots in this graph form a pattern, which reveals
that as income increases, expenditure increases.
Figure A1.4(b) shows the relationship between the
number of computers sold and the price of a computer. This graph shows that as the price of a computer
falls, the number of computers sold increases.
Figure A1.4(c) shows a scatter diagram of inflation and unemployment in the United States. Here,
the dots show no clear relationship between these two
variables. Dining out
Surfing the Internet
Playing cards
Baking
Doing crossword puzzles
Playing video games
Going to the zoo
Dancing
Attending rock concerts
Playing a musical instrument
0
10
20
30
Percentage of population 17 40 50 A crosssection graph shows the level of a variable across
categories or groups. This bar chart shows 10 popular
leisure activities and the percentage of the U.S. population
that engages in each of them.
animation 100 07
06 30 25 05
04
$23,862 02 A 99
20
0 98
97 03 01
00
$25,472 20
25
30
35
Income (thousands of dollars per year) (a) Expenditure and income 90
93 95 80 97
60
99
40 05 20 0 50 100
150
200
Computer sales (millions) (b) Computer sales and prices A scatter diagram reveals the relationship between two variables. Part (a) shows the relationship between expenditure
and income. Each point shows the values of the two variables in a specific year. For example, point A shows that in
2000, average income was $25,472 and average expenditure was $23,862. The pattern formed by the points
shows that as income increases, expenditure increases.
animation 00
03 Inflation rate (percent per year) Expenditure
(thousands of dollars per year) 35 Average computer price
(percentage of 1990 price) Scatter Diagrams FIGURE A1.4 6
00
06 4 07 05
01 08
04
03 99
2
98 0 4 02 5
6
7
Unemployment rate (percent) (c) Unemployment and inflation Part (b) shows the relationship between the price of a computer and the number of computers sold from 1990 to
2005. This graph shows that as the price of a computer
falls, the number of computers sold increases.
Part (c) shows a scatter diagram of the U.S. inflation rate and
the unemployment rate from 1998 to 2008. This graph shows
that inflation and unemployment are not closely related. 9160335_CH01_p001030.qxd 18 6/22/09 8:55 AM Page 18 CHAPTER 1 What Is Econom ics? Breaks in the Axes Two of the graphs you’ve just
looked at, Fig. A1.4(a) and Fig. A1.4(c), have breaks
in their axes, as shown by the small gaps. The breaks
indicate that there are jumps from the origin, 0, to
the first values recorded.
In Fig. A1.4(a), the breaks are used because the
lowest value of expenditure exceeds $20,000 and the
lowest value of income exceeds $20,000. With no
breaks in the axes, there would be a lot of empty
space, all the points would be crowded into the top
right corner, and we would not be able to see whether
a relationship exists between these two variables. By
breaking the axes, we are able to bring the relationship into view.
Putting a break in one or both axes is like using
a zoom lens to bring the relationship into the center
of the graph and magnify it so that the relationship
fills the graph.
Misleading Graphs Breaks can be used to highlight a relationship, but they can also be used to mislead—to
make a graph that lies. The most common way of
making a graph lie is to use axis breaks and to either
stretch or compress a scale. For example, suppose that
in Fig. A1.4(a), the yaxis that measures expenditure
ran from zero to $35,000 while the xaxis was the
same as the one shown. The graph would now create
the impression that despite a huge increase in income,
expenditure had barely changed.
To avoid being misled, it is a good idea to get
into the habit of always looking closely at the values
and the labels on the axes of a graph before you start
to interpret it. ◆ Graphs Used in
Economic Models
The graphs used in economics are not always designed
to show realworld data. Often they are used to show
general relationships among the variables in an economic model.
An economic model is a strippeddown, simplified
description of an economy or of a component of an
economy such as a business or a household. It consists of statements about economic behavior that can
be expressed as equations or as curves in a graph.
Economists use models to explore the effects of different policies or other influences on the economy in
ways that are similar to the use of model airplanes in
wind tunnels and models of the climate.
You will encounter many different kinds of
graphs in economic models, but there are some
repeating patterns. Once you’ve learned to recognize
these patterns, you will instantly understand the
meaning of a graph. Here, we’ll look at the different
types of curves that are used in economic models,
and we’ll see some everyday examples of each type of
curve. The patterns to look for in graphs are the four
cases in which
■ Variables move in the same direction. ■ Variables move in opposite directions. ■ Variables have a maximum or a minimum. ■ Variables are unrelated.
Let’s look at these four cases. Correlation and Causation A scatter diagram that shows a clear relationship between two variables, such
as Fig. A1.4(a) or Fig. A1.4(b), tells us that the two
variables have a high correlation. When a high correlation is present, we can predict the value of one variable from the value of the other variable. But
correlation does not imply causation.
Sometimes a high correlation is a coincidence,
but sometimes it does arise from a causal relationship. It is likely, for example, that rising income
causes rising expenditure (Fig. A1.4a) and that the
falling price of a computer causes more computers to
be sold (Fig. A1.4b).
You’ve now seen how we can use graphs in economics to show economic data and to reveal relationships. Next, we’ll learn how economists use
graphs to construct and display economic models. Variables That Move in the Same Direction
Figure A1.5 shows graphs of the relationships
between two variables that move up and down
together. A relationship between two variables that
move in the same direction is called a positive relationship or a direct relationship. A line that slopes
upward shows such a relationship.
Figure A1.5 shows three types of relationships,
one that has a straight line and two that have curved
lines. But all the lines in these three graphs are called
curves. Any line on a graph—no matter whether it is
straight or curved—is called a curve.
A relationship shown by a straight line is called
a linear relationship. Figure A1.5(a) shows a linear relationship between the number of miles traveled in 9160335_CH01_p001030.qxd 6/22/09 8:55 AM Page 19 Appendix: Graphs in Economics Positive
linear
relationship 300 A 200 100 0 40 Problems worked (number) 400 Positive (Direct) Relationships
Recovery time (minutes) Distance covered in 5 hours (miles) FIGURE A1.5 Positive,
becoming
steeper 30 20 40
60
80
Speed (miles per hour) (a) Positive linear relationship 0 20 Positive,
becoming
less steep 15 10 5 10 20 19 100 200
300
400
Distance sprinted (yards) (b) Positive, becoming steeper Each part of this figure shows a positive (direct) relationship
between two variables. That is, as the value of the variable
measured on the xaxis increases, so does the value of the
variable measured on the yaxis. Part (a) shows a linear
relationship—as the two variables increase together, we 0 2 4 6
8
Study time (hours) (c) Positive, becoming less steep move along a straight line. Part (b) shows a positive relationship such that as the two variables increase together, we
move along a curve that becomes steeper. Part (c) shows a
positive relationship such that as the two variables increase
together, we move along a curve that becomes flatter. animation 5 hours and speed. For example, point A shows that
we will travel 200 miles in 5 hours if our speed is 40
miles an hour. If we double our speed to 80 miles an
hour, we will travel 400 miles in 5 hours.
Figure A1.5(b) shows the relationship between
distance sprinted and recovery time (the time it takes
the heart rate to return to its normal resting rate).
This relationship is an upwardsloping one that
starts out quite flat but then becomes steeper as we
move along the curve away from the origin. The reason this curve slopes upward and becomes steeper is
because the additional recovery time needed from
sprinting an additional 100 yards increases. It takes
less than 5 minutes to recover from sprinting 100
yards but more than 10 minutes to recover from
sprinting 200 yards.
Figure A1.5(c) shows the relationship between
the number of problems worked by a student and
the amount of study time. This relationship is an
upwardsloping one that starts out quite steep and
becomes flatter as we move along the curve away
from the origin. Study time becomes less productive
as the student spends more hours studying and
becomes more tired. Variables That Move in
Opposite Directions
Figure A1.6 shows relationships between things that
move in opposite directions. A relationship between
variables that move in opposite directions is called a
negative relationship or an inverse relationship.
Figure A1.6(a) shows the relationship between
the hours spent playing squash and the hours spent
playing tennis when the total number of hours available is 5. One extra hour spent playing tennis means
one hour less playing squash and vice versa. This relationship is negative and linear.
Figure A1.6(b) shows the relationship between
the cost per mile traveled and the length of a journey.
The longer the journey, the lower is the cost per mile.
But as the journey length increases, even though the
cost per mile decreases, the fall in the cost is smaller
the longer the journey. This feature of the relationship is shown by the fact that the curve slopes downward, starting out steep at a short journey length and
then becoming flatter as the journey length increases.
This relationship arises because some of the costs are
fixed, such as auto insurance, and the fixed costs are
spread over a longer journey. 9160335_CH01_p001030.qxd 6/22/09 8:55 AM Page 20 CHAPTER 1 What Is Econom ics? Negative (Inverse) Relationships 5
Negative
linear
relationship 4
3
2
1 0 50
Negative,
becoming
less steep 40
30
20
10 1 2
3
4
5
Time playing tennis (hours) (a) Negative linear relationship 0 Problems worked (number) Time playing squash (hours) FIGURE A1.6 Travel cost (cents per mile) 20 25
Negative,
becoming
steeper 20
15
10
5 100 200 300 400
500
Journey length (miles) (b) Negative, becoming less steep Each part of this figure shows a negative (inverse) relationship between two variables. That is, as the value of the
variable measured on the xaxis increases, the value of the
variable measured on the yaxis decreases. Part (a) shows
a linear relationship. The total time spent playing tennis
and squash is 5 hours. As the time spent playing tennis
increases, the time spent playing squash decreases, and 0 2 4 6
10
8
Leisure time (hours) (c) Negative, becoming steeper we move along a straight line. Part (b) shows a negative
relationship such that as the journey length increases, the
travel cost decreases as we move along a curve that
becomes less steep. Part (c) shows a negative relationship
such that as leisure time increases, the number of problems
worked decreases as we move along a curve that
becomes steeper. animation Figure A1.6(c) shows the relationship between
the amount of leisure time and the number of problems worked by a student. Increasing leisure time
produces an increasingly large reduction in the number of problems worked. This relationship is a negative one that starts out with a gentle slope at a small
number of leisure hours and becomes steeper as the
number of leisure hours increases. This relationship is
a different view of the idea shown in Fig. A1.5(c). Variables That Have a Maximum
or a Minimum
Many relationships in economic models have a maximum or a minimum. For example, firms try to make
the maximum possible profit and to produce at the
lowest possible cost. Figure A1.7 shows relationships
that have a maximum or a minimum.
Figure A1.7(a) shows the relationship between rainfall and wheat yield. When there is no rainfall, wheat
will not grow, so the yield is zero. As the rainfall
increases up to 10 days a month, the wheat yield increases. With 10 rainy days each month, the wheat
yield reaches its maximum at 40 bushels an acre (point
A). Rain in excess of 10 days a month starts to lower the
yield of wheat. If every day is rainy, the wheat suffers
from a lack of sunshine and the yield decreases to zero.
This relationship is one that starts out sloping upward,
reaches a maximum, and then slopes downward.
Figure A1.7(b) shows the reverse case—a relationship that begins sloping downward, falls to a
minimum, and then slopes upward. Most economic
costs are like this relationship. An example is the relationship between the cost per mile and speed for a car
trip. At low speeds, the car is creeping in a traffic
snarlup. The number of miles per gallon is low, so
the cost per mile is high. At high speeds, the car is
traveling faster than its efficient speed, using a large
quantity of gasoline, and again the number of miles
per gallon is low and the cost per mile is high. At a
speed of 55 miles an hour, the cost per mile is at its
minimum (point B). This relationship is one that
starts out sloping downward, reaches a minimum,
and then slopes upward. 9160335_CH01_p001030.qxd 6/22/09 8:55 AM Page 21 A ppendix: Graphs in Economics Maximum and Minimum Points
Maximum
yield 50 A 40
30
20 Increasing
yield Gasoline cost (cents per mile) Wheat yield (bushels per acre) FIGURE A1.7 15 Decreasing
cost Increasing
cost 10 Decreasing
yield Minimum
cost B 5 10 0 5 10 21 30
15
20
25
Rainfall (days per month) (a) Relationship with a maximum 0 15 35 95
55
75
Speed (miles per hour) Part (a) shows a relationship that has a maximum
point, A. The curve
slopes upward as it rises
to its maximum point, is
flat at its maximum, and
then slopes downward.
Part (b) shows a
relationship with a minimum point, B. The curve
slopes downward as it
falls to its minimum, is
flat at its minimum, and
then slopes upward. (b) Relationship with a minimum animation Variables That Are Unrelated
There are many situations in which no matter what
happens to the value of one variable, the other variable remains constant. Sometimes we want to show
the independence between two variables in a graph,
and Fig. A1.8 shows two ways of achieving this. Variables That Are Unrelated 100 75 Unrelated:
y constant 50 25 0 20 40
60
80
Price of bananas (cents per pound) (a) Unrelated: y constant animation Rainfall in California (days per month) Grade in economics (percent) FIGURE A1.8 In describing the graphs in Fig. A1.5 through
A1.7, we have talked about curves that slope upward
or slope downward, and curves that become less steep
or steeper. Let’s spend a little time discussing exactly
what we mean by slope and how we measure the
slope of a curve. 20 15 Unrelated:
x constant 10 5 0 1
2
3
4
Output of French wine (billions of gallons) (b) Unrelated: x constant This figure shows how
we can graph two variables that are unrelated.
In part (a), a student’s
grade in economics is
plotted at 75 percent on
the yaxis regardless of
the price of bananas on
the xaxis. The curve is
horizontal.
In part (b), the output
of the vineyards of France
on the xaxis does not
vary with the rainfall in
California on the yaxis.
The curve is vertical. 9160335_CH01_p001030.qxd 6/22/09 8:55 AM Page 22 CHAPTER 1 What Is Econom ics? 22 ◆ The Slope of a Relationship If a large change in the variable measured on the
yaxis ( y) is associated with a small change in the
variable measured on the xaxis ( x), the slope is
large and the curve is steep. If a small change in the
variable measured on the yaxis ( y) is associated
with a large change in the variable measured on the
xaxis ( x), the slope is small and the curve is flat.
We can make the idea of slope clearer by doing
some calculations. We can measure the influence of one variable on
another by the slope of the relationship. The slope of
a relationship is the change in the value of the variable measured on the yaxis divided by the change in
the value of the variable measured on the xaxis. We
use the Greek letter (delta) to represent “change
in.” Thus y means the change in the value of the
variable measured on the yaxis, and x means the
change in the value of the variable measured on the
xaxis. Therefore the slope of the relationship is The Slope of a Straight Line
The slope of a straight line is the same regardless of
where on the line you calculate it. The slope of a
straight line is constant. Let’s calculate the slopes of
the lines in Fig. A1.9. In part (a), when x increases ¢ y/ ¢ x. FIGURE A1.9 The Slope of a Straight Line y y
8 8
3 Slope = —
4 7 3 Slope = – —
4 7 6 6 5 5 y=3 ∇ 4 4 3 3 2 2 ∇
∇ 0 ∇ x=4 1 y = –3
x=4 1
1 2 3 4 5 6 7 8 x (a) Positive slope 0 1 2 3 4 5 6 7 8 x (b) Negative slope To calculate the slope of a straight line, we divide the
change in the value of the variable measured on the yaxis
( y) by the change in the value of the variable measured
on the xaxis ( x) as we move along the curve.
Part (a) shows the calculation of a positive slope. When
x increases from 2 to 6, x equals 4. That change in x
animation brings about an increase in y from 3 to 6, so y equals 3.
The slope ( y/ x) equals 3/4.
Part (b) shows the calculation of a negative slope. When
x increases from 2 to 6, x equals 4. That increase in x
brings about a decrease in y from 6 to 3, so y equals –3.
The slope ( y/ x) equals –3/4. 9160335_CH01_p001030.qxd 6/22/09 8:55 AM Page 23 Appendix: Graphs in Economics from 2 to 6, y increases from 3 to 6. The change in
x is +4—that is, x is 4. The change in y is +3—that
is, y is 3. The slope of that line is
¢y
¢x = 3
.
4 In part (b), when x increases from 2 to 6, y
decreases from 6 to 3. The change in y is minus 3—
that is, y is –3. The change in x is plus 4—that is,
x is 4. The slope of the curve is FIGURE A1.10 Slope at a Point y
8
7
3
Slope = —
4 6 A
5
4
∇ 3
=
.
¢x
4
Notice that the two slopes have the same magnitude
(3/4), but the slope of the line in part (a) is positive
(+3/+4 = 3/4) while that in part (b) is negative
(–3/+4 = –3/4). The slope of a positive relationship is
positive; the slope of a negative relationship is negative. The Slope of a Curved Line
The slope of a curved line is trickier. The slope of a
curved line is not constant, so the slope depends on
where on the curved line we calculate it. There are
two ways to calculate the slope of a curved line: You
can calculate the slope at a point, or you can calculate
the slope across an arc of the curve. Let’s look at the
two alternatives. y=3 3
2
1 0 ∇ ¢y 23 1 x=4 2 3 4 5 6 7 8 x To calculate the slope of the curve at point A, draw the red
line that just touches the curve at A—the tangent. The slope
of this straight line is calculated by dividing the change in y
by the change in x along the line. When x increases from
0 to 4, x equals 4. That change in x is associated with an
increase in y from 2 to 5, so y equals 3. The slope of the
red line is 3/4. So the slope of the curve at point A is 3/4.
animation Slope at a Point To calculate the slope at a point on a curve, you need to construct a straight line that has
the same slope as the curve at the point in question.
Figure A1.10 shows how this is done. Suppose you
want to calculate the slope of the curve at point A.
Place a ruler on the graph so that it touches point A
and no other point on the curve, then draw a straight
line along the edge of the ruler. The straight red line
is this line, and it is the tangent to the curve at point
A. If the ruler touches the curve only at point A, then
the slope of the curve at point A must be the same as
the slope of the edge of the ruler. If the curve and the
ruler do not have the same slope, the line along the
edge of the ruler will cut the curve instead of just
touching it.
Now that you have found a straight line with the
same slope as the curve at point A, you can calculate
the slope of the curve at point A by calculating the
slope of the straight line. Along the straight line, as x increases from 0 to 4 ( x = 4) y increases from 2 to 5
( y = 3). Therefore the slope of the straight line is
¢y
¢x = 3
.
4 So the slope of the curve at point A is 3/4.
Slope Across an Arc An arc of a curve is a piece of a curve. In Fig. A1.11, you are looking at the same
curve as in Fig. A1.10. But instead of calculating the
slope at point A, we are going to calculate the slope
across the arc from B to C. You can see that the slope
at B is greater than at C. When we calculate the slope
across an arc, we are calculating the average slope
between two points. As we move along the arc from
B to C, x increases from 3 to 5 and y increases from 4
to 5.5. The change in x is 2 ( x 2), and the change 9160335_CH01_p001030.qxd 6/22/09 8:55 AM Page 24 CHAPTER 1 What Is Econom ics? 24 ◆ Graphing Relationships Among Slope Across an Arc FIGURE A1.11 More Than Two Variables y
8.0
7.0
1.5 3 Slope = — = —
2
4 6.0 C 5.5 A 5.0 ∇ y = 1.5 B 4.0
3.0 x=2 ∇ 2.0
1.0 0 1 2 3 4 5 6 7 8 x To calculate the average slope of the curve along the arc
BC, draw a straight line from B to C. The slope of the line
BC is calculated by dividing the change in y by the change
in x. In moving from B to C, x equals 2 and y equals
1.5. The slope of the line BC is 1.5 divided by 2, or 3/4.
So the slope of the curve across the arc BC is 3/4. Ceteris Paribus Ceteris paribus means “if all other rel animation in y is 1.5 ( y 1.5). Therefore the slope is
¢y
¢x = We have seen that we can graph the relationship
between two variables as a point formed by the xand ycoordinates in a twodimensional graph. You
might be thinking that although a twodimensional
graph is informative, most of the things in which you
are likely to be interested involve relationships among
many variables, not just two. For example, the
amount of ice cream consumed depends on the price
of ice cream and the temperature. If ice cream is
expensive and the temperature is low, people eat
much less ice cream than when ice cream is inexpensive and the temperature is high. For any given price
of ice cream, the quantity consumed varies with the
temperature; and for any given temperature, the
quantity of ice cream consumed varies with its price.
Figure A1.12 shows a relationship among three
variables. The table shows the number of gallons of
ice cream consumed each day at various temperatures and ice cream prices. How can we graph these
numbers?
To graph a relationship that involves more than
two variables, we use the ceteris paribus assumption. 1.5
3
=.
2
4 So the slope of the curve across the arc BC is 3/4.
This calculation gives us the slope of the curve
between points B and C. The actual slope calculated
is the slope of the straight line from B to C. This
slope approximates the average slope of the curve
along the arc BC. In this particular example, the
slope across the arc BC is identical to the slope of the
curve at point A. But the calculation of the slope of a
curve does not always work out so neatly. You might
have fun constructing some more examples and a few
counterexamples.
You now know how to make and interpret a
graph. But so far, we’ve limited our attention to
graphs of two variables. We’re now going to learn
how to graph more than two variables. evant things remain the same.” To isolate the relationship of interest in a laboratory experiment, we
hold other things constant. We use the same method
to graph a relationship with more than two variables.
Figure A1.12(a) shows an example. There, you
can see what happens to the quantity of ice cream
consumed when the price of ice cream varies and
the temperature is held constant. The line labeled
70°F shows the relationship between ice cream consumption and the price of ice cream if the temperature remains at 70°F. The numbers used to plot that
line are those in the third column of the table in
Fig. A1.12. For example, if the temperature is 70°F,
10 gallons are consumed when the price is 60¢ a
scoop, and 18 gallons are consumed when the price
is 30¢ a scoop. The curve labeled 90°F shows consumption as the price varies if the temperature
remains at 90°F.
We can also show the relationship between ice
cream consumption and temperature when the
price of ice cream remains constant, as shown in
Fig. A1.12(b). The curve labeled 60¢ shows how the
consumption of ice cream varies with the temperature 9160335_CH01_p001030.qxd 6/22/09 8:55 AM Page 25 Appendix: Graphs in Economics 100
80
60
40 0 60¢ 70
15¢
50
30 90ºF
20 90 Temperature (degrees F) Graphing a Relationship Among Three Variables
Temperature (degrees F) Price (cents per scoop) FIGURE A1.12 25 90
10 gallons
70
7 gallons 50
30 70ºF
10 20 40
60
Ice cream consumption
(gallons per day) (a) Price and consumption at
a given temperature 0 10 (b) Temperature and consumption
at a given price Ice cream consumption
Price (gallons per day) 30°F 50°F 70°F 90°F 15 12 18 25 50 30 10 12 18 37 45 7 10 13 27 60 5 7 10 20 75 3 5 7 14 90 2 3 5 10 105 1 2 3 6 (cents per scoop) 40
20
Ice cream consumption
(gallons per day) 0 20 40 80
100
60
Price (cents per scoop) (c) Temperature and price at
a given consumption Ice cream consumption depends on its price and the temperature. The table tell us how many gallons of ice cream are
consumed each day at different prices and different temperatures. For example, if the price is 60¢ a scoop and the
temperature is 70ºF, 10 gallons of ice cream are consumed.
This set of values is highlighted in the table and each part of
the figure.
To graph a relationship among three variables, the
value of one variable is held constant. Part (a) shows the
relationship between price and consumption when temperature is held constant. One curve holds temperature at 90ºF
and the other holds it at 70ºF. Part (b) shows the relationship between temperature and consumption when price is
held constant. One curve holds the price at 60¢ a scoop
and the other holds it at 15¢ a scoop. Part (c) shows the
relationship between temperature and price when consumption is held constant. One curve holds consumption at 10
gallons and the other holds it at 7 gallons. animation when the price of ice cream is 60¢ a scoop, and a second curve shows the relationship when the price is
15¢ a scoop. For example, at 60¢ a scoop, 10 gallons
are consumed when the temperature is 70°F and 20
gallons are consumed when the temperature is 90°F.
Figure A1.12(c) shows the combinations of temperature and price that result in a constant consumption of ice cream. One curve shows the combinations
that result in 10 gallons a day being consumed, and
the other shows the combinations that result in 7
gallons a day being consumed. A high price and a high temperature lead to the same consumption as a
lower price and a lower temperature. For example, 10
gallons of ice cream are consumed at 70°F and 60¢ a
scoop, at 90°F and 90¢ a scoop, and at 50°F and 45¢
a scoop. ◆ With what you have learned about graphs, you can move forward with your study of economics.
There are no graphs in this book that are more complicated than those that have been explained in this
appendix. 9160335_CH01_p001030.qxd 6/22/09 8:55 AM Page 26 CHAPTER 1 What Is Econom ics? 26 MATHEMATICAL NOTE ◆ Equations of Straight Lines
If a straight line in a graph describes the relationship
between two variables, we call it a linear relationship.
Figure 1 shows the linear relationship between a person’s
expenditure and income. This person spends $100 a
week (by borrowing or spending previous savings)
when income is zero. And out of each dollar earned,
this person spends 50 cents (and saves 50 cents).
All linear relationships are described by the same
general equation. We call the quantity that is measured
on the horizontal axis (or xaxis) x, and we call the
quantity that is measured on the vertical axis (or yaxis)
y. In the case of Fig. 1, x is income and y is expenditure. straight line hits the yaxis at a value equal to a.
Figure 1 illustrates the yaxis intercept.
For positive values of x, the value of y exceeds a.
The constant b tells us by how much y increases
above a as x increases. The constant b is the slope of
the line. Slope of Line
As we explain in the chapter, the slope of a relationship is the change in the value of y divided by the
change in the value of x. We use the Greek letter
(delta) to represent “change in.” So y means the
change in the value of the variable measured on the
yaxis, and x means the change in the value of the
variable measured on the xaxis. Therefore the slope
of the relationship is
y/ x. A Linear Equation y a bx. Expenditure (dollars per week) In this equation, a and b are fixed numbers and they
are called constants. The values of x and y vary, so
these numbers are called variables. Because the equation describes a straight line, the equation is called a
linear equation.
The equation tells us that when the value of x is
zero, the value of y is a. We call the constant a the
yaxis intercept. The reason is that on the graph the 400 y = a + bx Value of y
Slope = b 300 200 To see why the slope is b, suppose that initially
the value of x is x1, or $200 in Fig. 2. The corresponding value of y is y1, also $200 in Fig. 2. The equation of the line tells us that
y1 a bx 1. (1) Now the value of x increases by x to x 1 + x
(or $400 in Fig. 2). And the value of y increases by
y to y 1 + y (or $300 in Fig. 2).
The equation of the line now tells us that
y y1
Expenditure (dollars per week) The equation that describes a straightline relationship between x and y is a b(x 1 x) 400 y1 + Δy
300
Δy
200 y1
100 0 yaxis
intercept = a
100 200 Value of x 100 Δx x1
300
400
500
Income (dollars per week) Figure 1 Linear relationship 0 100 200 x 1 + Δx 300
400
500
Income (dollars per week) Figure 2 Calculating slope (2) 9160335_CH01_p001030.qxd 6/22/09 8:55 AM Page 27 M athematical Note To calculate the slope of the line, subtract equation
(1) from equation (2) to obtain
y bx (3) and now divide equation (3) by x to obtain
y/ x relationships have a slope that is positive. In the
equation of the line, the constant b is positive. In this
example, the yaxis intercept, a, is 100. The slope b
equals y/ x, which in Fig. 2 is 100/200 or 0.5. The
equation of the line is
y b. 100 Position of Line
The yaxis intercept determines the position of the
line on the graph. Figure 3 illustrates the relationship
between the yaxis intercept and the position of the
line. In this graph, the yaxis measures saving and the
xaxis measures income.
When the yaxis intercept, a, is positive, the line
hits the yaxis at a positive value of y—as the blue line
does. Its yaxis intercept is 100. When the yaxis intercept, a, is zero, the line hits the yaxis at the origin—
as the purple line does. Its yaxis intercept is 0. When
the yaxis intercept, a, is negative, the line hits the
yaxis at a negative value of y—as the red line does. Its
yaxis intercept is –100.
As the equations of the three lines show, the value
of the yaxis intercept does not influence the slope of
the line. All three lines have a slope equal to 0.5. Figure 4 shows a negative relationship—the two variables x and y move in the opposite direction. All negative relationships have a slope that is negative. In the
equation of the line, the constant b is negative. In the
example in Fig. 4, the yaxis intercept, a, is 30. The
slope, b, equals y/ x, which is –20/2 or –10. The
equation of the line is
y 30 Positive Relationships
Figure 1 shows a positive relationship—the two variables x and y move in the same direction. All positive ( 10)x or
y 30 10x. Example
A straight line has a yaxis intercept of 50 and a slope
of 2. What is the equation of this line?
The equation of a straight line is
y Saving (dollars per week) 0.5x. Negative Relationships So the slope of the line is b. a bx where a is the yaxis intercept and b is the slope.
So the equation is
y 50 2x.
y 300 Positive yaxis
intercept, a = 100 y = 100 + 0.5x 200 y = 0.5x 100 20 Positive yaxis
intercept, a = 30 y = –100 + 0.5x 30
Slope, b = –10 20
0
–100
–200 100 200 300 400 500 600
Income (dollars per week) 10 Negative yaxis
intercept, a = –100 y = 30 – 10x
0 Figure 3 The yaxis intercept 27 1 2 Figure 4 Negative relationship x 9160335_CH01_p001030.qxd 28 6/22/09 8:55 AM Page 28 CHAPTER 1 What Is Econom ics? Review Quiz ◆
1
2
3
4 5 What are the three types of graphs used to show
economic data?
Give an example of a timeseries graph.
List three things that a timeseries graph shows
quickly and easily.
Give three examples, different from those in the
chapter, of scatter diagrams that show a positive
relationship, a negative relationship, and no
relationship.
Draw some graphs to show the relationships
between two variables
a. That move in the same direction. SUMMARY 6 7
8 Work Study Plan 1.A
and get instant feedback. ◆ Key Points The Slope of a Relationship (pp. 22–24)
■ Graphing Data (pp. 15–18)
■ ■ ■ A timeseries graph shows the trend and fluctuations in a variable over time.
A crosssection graph shows how the value of a variable changes across the members of a population.
A scatter diagram shows the relationship between
two variables. It shows whether two variables are
positively related, negatively related, or unrelated. Graphs Used in Economic Models (pp. 18–21)
■ ■ b. That move in opposite directions.
c. That have a maximum.
d. That have a minimum.
Which of the relationships in question 5 is a
positive relationship and which is a negative
relationship?
What are the two ways of calculating the slope
of a curved line?
How do we graph a relationship among more
than two variables? Graphs are used to show relationships among variables in economic models.
Relationships can be positive (an upwardsloping
curve), negative (a downwardsloping curve), positive and then negative (have a maximum point),
negative and then positive (have a minimum point),
or unrelated (a horizontal or vertical curve). ■
■ The slope of a relationship is calculated as the
change in the value of the variable measured on
the yaxis divided by the change in the value of the
variable measured on the xaxis—that is, y/ x.
A straight line has a constant slope.
A curved line has a varying slope. To calculate the
slope of a curved line, we calculate the slope at a
point or across an arc. Graphing Relationships Among More Than Two
Variables (pp. 24–25)
■ ■ To graph a relationship among more than two
variables, we hold constant the values of all the
variables except two.
We then plot the value of one of the variables
against the value of another. Key Figures
Figure A1.1
Figure A1.5
Figure A1.6
Figure A1.7 Making a Graph, 15
Positive (Direct) Relationships, 19
Negative (Inverse) Relationships, 20
Maximum and Minimum Points, 21 Figure A1.9 The Slope of a Straight Line, 22
Figure A1.10 Slope at a Point, 23
Figure A1.11 Slope Across an Arc, 24 Key Terms
Ceteris paribus, 24
Crosssection graph, 16
Direct relationship, 18
Inverse relationship, 19 Linear relationship, 18
Negative relationship, 19
Positive relationship, 18
Scatter diagram, 17 Slope, 22
Timeseries graph, 16
Trend, 16 9160335_CH01_p001030.qxd 6/22/09 8:55 AM Page 29 P roblems and Applications PROBLEMS and APPLICATIONS 29 ◆ Work problems 1–5 in Chapter 1A Study Plan and get instant feedback.
Work problems 6–10 as Homework, a Quiz, or a Test if assigned by your instructor. 1. The spreadsheet provides data on the U.S. economy: Column A is the year, column B is the inflation rate, column C is the interest rate, column D
is the growth rate, and column E is the unemployment rate. 3. Calculate the slope of the following relationship.
y
10
8 A B C D E 1 1997 2.8 7.6 2.5 5.6 2 1998 2.9 7.4 3.7 5.4 3 1999 2.3 7.3 4.5 4.9 4 2000 1.6 6.5 4.2 4.5 5 2001 2.2 7.0 4.4 4.2 6 2002 3.4 7.6 3.7 4.0 7 2003 2.8 7.1 0.8 4.7 8 2004 1.6 6.5 3.6 5.8 9 2005 2.3 5.7 3.1 6.0 10 2006 2.5 5.6 2.9 4.6 11 2007 4.1 5.6 2.2 4.6 a. Draw a timeseries graph of the inflation rate.
b. In which year(s) (i) was inflation highest, (ii)
was inflation lowest, (iii) did it increase, (iv) did
it decrease, (v) did it increase most, and (vi) did
it decrease most?
c. What was the main trend in inflation?
d. Draw a scatter diagram of the inflation rate and
the interest rate. Describe the relationship.
e. Draw a scatter diagram of the growth rate and
the unemployment rate. Describe the relationship.
2. ‘Hulk’ Tops Box Office With Sales of $54.5
Million:
Theaters
Movie Hulk
The Happening
Zohan
Crystal Skull Revenue (number) 6
4
2 0 4.0 8.0 x 4. Calculate the slope of the following relationship:
a. At point A and at point B.
b. Across the arc AB.
y
10.0
8.0 A 6.0
4.0 B 1.5
0 2 4 6 8 10 x 5. The table gives the price of a balloon ride, the
temperature, and the number of rides a day. (dollars per theater) 3,505
15,560
2,986
10,214
3,462
4,737
3,804
3,561
Bloomberg.com, June 15, 2008
a. Draw a graph to show the relationship between
the revenue per theater on the yaxis and the
number of theaters on the xaxis. Describe the
relationship.
b. Calculate the slope of the relationship between
3,462 and 3,804 theaters. 12.0 Balloon rides
(number per day) Price
(dollars per ride) 50ºF 70ºF 90ºF 5
32
40
50
10
27
32
40
15
18
27
32
Draw graphs to show the relationship between
a. The price and the number of rides, holding the
temperature constant. Describe this relationship.
b. The number of rides and temperature, holding
the price constant. 9160335_CH01_p001030.qxd 6/22/09 8:55 AM Page 30 CHAPTER 1 What Is Econom ics? 30 6. The spreadsheet provides data on oil and gasoline: Column A is the year, column B is the price
of oil (dollars per barrel), column C is the price
of gasoline (cents per gallon), column D is U.S.
oil production, and column E is the U.S. quantity of gasoline refined (both in millions of barrels per day).
A B C D E 1 1997 16 117 2.35 1998 9 98 2.28 1999 24 131 2.15 8.3 4 2000 22 145 2.13 8.0 5 2001 18 111 2.12 8.3 6 2002 30 144 2.10 8.8 7 2003 28 153 2.07 8.7 8 2004 36 184 1.98 9.2 A 8.3 3 y
18 8.3 2 8. Calculate the slope of the following relationship
at point A. 9 2005 52 224 1.89 8.9 10 2006 57 239 1.86 9.4 11 2007 90 303 1.86 10 0 4 x 9 9. Calculate the slope of the following relationship:
a. At point A and at point B.
b. Across the arc AB. 9.1 y a. Draw a timeseries graph of the quantity of
gasoline refined.
b. In which year(s) (i) was the quantity of gasoline refined highest, (ii) was it lowest, (iii) did
it increase, (iv) did it decrease, (v) did it
increase most, and (vi) did it decrease most?
c. What was the main trend in this quantity?
d. Draw a scatter diagram of the price of oil and
the quantity of oil. Describe the relationship.
e. Draw a scatter diagram of the price of gasoline
and the quantity of gasoline. Describe the
relationship.
7. Draw a graph that shows the relationship
between the two variables x and y:
x
y 0
25 1
24 2
22 3
18 4
12 5
0 a. Is the relationship positive or negative?
b. Does the slope of the relationship increase or
decrease as the value of x increases?
c. Think of some economic relationships that
might be similar to this one.
d. Calculate the slope of the relationship
between x and y when x equals 3.
e. Calculate the slope of the relationship across
the arc as x increases from 4 to 5. A 6 4 B 2 0 1 2 3 4 5 x 10. The table gives information about umbrellas:
price, the number purchased, and rainfall.
Umbrellas
(number per day) Price
(dollars
per umbrella) 0 20
30
40 4
2
1 1 2 (inches of rainfall) 7
4
2 8
7
4 Draw graphs to show the relationship between
a. Price and the number of umbrellas purchased,
holding the amount of rainfall constant.
Describe this relationship.
b. The number of umbrellas purchased and the
amount of rainfall, holding the price constant.
Describe this relationship. ...
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This note was uploaded on 02/07/2010 for the course ECON 251 taught by Professor Blanchard during the Fall '08 term at Purdue UniversityWest Lafayette.
 Fall '08
 Blanchard
 Microeconomics

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