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ECONOMICS 175
Professor Ronald D. Lee
1/22/09
Lecture 2
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Professor Lee is not here today so I am taking his
place. My name is Professor Wilmoth. Please see
the lecture notes on bSpace for the readings due for
next Tuesday. The GSIs will not hold office hours
next week. Please go to the computer sections if
you need help with the problem set. Next week all
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LECTURE
Population Balance Equation
The idea is things have to add up over time. If you
take the population at time 1 and 2, the difference
has to be explained by births, deaths and
immigrations. For example, during 2006, the
population was 6.555 billion. In 2007 the
population was 6.625 billion. The difference
between the two is .070 billion (70 million).
To compute a growth rate, you take this increment
over the average population size during the year. So
take .07/6.590 which gives you .011. This means
that the population has grown 1.1% a year. Make
sure the decimal places are the same in the
numerator and denominator.
There is another way to look at it. The 70 million
population increase represents .129 births minus
.059 deaths in 2006.
Pop(2007) Pop(2006) = Birth(2006) – Death(2006)
If you divide both sides by the average population
you will get the rate of growth. If you take the right
hand side of the equation by the average population
size and this gives you the
crude birth rate
and
the
crude death rate.
r = cbr – cdr
[rate of growth = crude birth rate – crude death rate]
This tells you how many births were added to the
population per individual already living and how
many people died per people already living in the
population. The difference between the two gives
you the
rate of growth
(r). If this were not the
world population, you would need to figure in
numbers for migration. Since we are looking at the
world, we do not have migration to and from the
world so we do not need to take this into account.
Historical Population Growth Rates
(Graph: world population growth rates from 1500
2150.)
What is interesting is for hundreds and
thousands of years, the population barely grew. You
look at this graph that starts in 1515 and the growth
rate is already up to .3% which is much higher than
historical values. Already in this era population
growth had started to take off compared to previous
periods. But this rate of increase is still small
compared to what has happened since 1950. After
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 Spring '08
 Lee
 Economics

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