2.1 Looking at Data—Relationships
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Looking at Data—Relationships
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CHAPTER OUTLINE
2.1 Relationships
2.2 Scatterplots
2.3 Correlation
2.4 Least-Squares Regression
2.5 Cautions about Correlation and Regression
2.6 Data Analysis for Two-Way Tables
2.7 The Question of Causation
Introduction
In Chapter 1, we learned to use graphical and numerical methods to describe the distribution of a single variable. Many of the interesting examples of the use of statistics involve relationships between pairs of variables. Learning ways to describe relationships with graphical and numerical methods is the focus of this chapter.
In Section 2.2, we focus on graphical descriptions. The scatterplot is our fundamental graphical tool for displaying the relationship between two quantitative variables. Sections 2.3 and 2.4 move on to numerical summaries for these relationships. Cautions about the use of these methods are discussed in Section 2.5. Graphical and numerical methods for describing the relationship between two categorical variables are presented in Section 2.6. We conclude with Section 2.7, a brief overview of issues related to the distinction between associations and causation.