L7-ss - The UNIVERSITY of NORTH CAROLINA at CHAPEL HILL...

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5/18/11 Lecture 7 1 STOR 155 Introductory Statistics Lecture 7: Scatterplots, Correlation The UNIVERSITY of NORTH CAROLINA at CHAPEL HILL
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5/18/11 Lecture 7 2 Relationships between Quantitative Variables • Chapter 1 talks about distribution of one variable. • Often we are interested in the relationships between two quantitative variables. • Examples: – Heights of parents and children – High school GPA and college GPA – Stock returns of two different corporations
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5/18/11 Lecture 7 3 Chapter 2: Looking at Data – Relationships • Association (statistical dependence) • Response and explanatory variables • Scatterplots • Correlation
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5/18/11 Lecture 7 4 Association between Variables • Two variables are associated (dependent) if some values of one variable tend to occur more often along with some values of the second variable .
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5/18/11 Lecture 7 5 Positive vs Negative Association
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5/18/11 Lecture 7 6 Examples • weight (in kilogram) and height (in centimeter) • An insurance company reports that heavier cars have less fatal accidents per 10,000 vehicles than lighter cars do. • A medical study finds that short women are more likely to have heart attacks than women of average height, while tall women have even fewer heart attacks. Note: no explanation yet, just findings …
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5/18/11 Lecture 7 7 Response and Explanatory Variables • A response variable (or dependent variable ) measures an outcome of a study • An
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L7-ss - The UNIVERSITY of NORTH CAROLINA at CHAPEL HILL...

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