Chapter 1 ECON 261.docx - Chapter 1 ECON 261 1.1...

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Chapter 1 ECON 261 1.1 Individuals and variables This page includes Statistical Videos This page includes Video Technology Manuals Any set of data contains information about some group of individuals . The information is organized in variables . Individuals and Variables Individuals are the objects described by a set of data. Individuals may be people, but they may also be animals or things. A variable is any characteristic of an individual. A variable can take different values for different individuals. A college’s student database, for example, includes data about every currently enrolled student. The students are the individuals described by the data set. For each individual, the data contain the values of variables such as date of birth, choice of major, and grade point average (GPA). In practice, any set of data is accompanied by background information that helps us understand the data. When you plan a statistical study or explore data from someone else’s work, ask yourself the following questions: DATA The documentary Particle Fever recreates the excitement of the Large Hadron Collider (LHC) experiment . The LHC is a 17 mile tunnel, designed to accelerate a proton to close to the speed of light, and then have protons collide to help physicists understand how the universe works. When the first collisions are recorded live in the film, American physicist Monica Dunford exclaims, “We have data. It’s unbelievable how fantastic this data is.” 1. Who? What individuals do the data describe? How many individuals appear in the data? 2. What? How many variables do the data contain? What are the exact definitions of these variables? In what unit of measurement is each variable recorded? Weights, for example, might be recorded in pounds, in thousands of pounds, or in kilograms. 3. Where? Student GPAs and SAT scores (or lack of them) will vary from college to college depending on many variables, including admissions “selectivity” for the college.
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4. When? Students change from year to year, as do prices, salaries, and so forth. 5. Why? What purpose do the data have? Do we hope to answer some specific questions? Do we want answers for just these individuals or for some larger group that these individuals are supposed to represent? Are the individuals and variables suitable for the intended purpose? Some variables, such as a person’s sex or college major, simply place individuals into categories. Others, like height and GPA, take numerical values for which we can do arithmetic. It makes sense to give an average income for a company’s employees, but it does not make sense to give an “average” sex. We can, however, count the numbers of female and male employees and do arithmetic with these counts. Categorical and Quantitative Variables A categorical variable places an individual into one of several groups or categories.
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