Chapter 15

Correlation: The Rise and Fall of Relationships

In This Chapter

Understanding what correlation is all about

Discovering how correlation connects to regression

Drawing conclusions from correlations

Analyzing items

In Chapter 14, I show you the ins and outs of regression, a tool for summarizing relationships between (and among) variables. In this chapter, I introduce you to the ups and downs of correlation, another tool for looking at relationships.

I use the example of SAT and GPA from Chapter 14, and show how to think about the data in a slightly different way. The new concepts connect to what I show you in the preceding chapter, and you’ll see how that works. I also show you how to test hypotheses about relationships and how to use Excel functions and data analysis tools for correlation.

Scatterplots Again

A scatterplot is a graphic way of showing a relationship between two variables. Figure 15-1 is a scatterplot that represents the GPAs and SAT scores of 20 students at the fictional Sahutsket University. The GPAs are on a 4.0 scale and the SATs are combined Verbal ...

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