Chapter 7
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 6 of Book 3, I introduce the concept of regression, a tool for summarizing and testing 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 employee aptitude and performance from Chapter 6 of Book 3 and show how to think about the data in a slightly different way. The new concepts connect to what I show you in Chapter 6 of Book 3 and you’ll see how those connections work. I also show you how to test hypotheses about relationships and how to use R functions for correlation.
Understanding Correlation
A scatterplot is a graphical way of showing a relationship between two variables. In Chapter 6 of Book 3, I show you a scatterplot of the data for employees at FarMisht Consulting, Inc. I reproduce that scatterplot here as
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