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 introduce the concepts 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 14 and show how to think about the data in a slightly different way. The new concepts connect to what I show you in Chapter 14, 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.

## Scatter plots Again

A scatter plot is a graphical way of showing a relationship between two variables. In Chapter 14, I show you a scatter plot of the data for employees at FarMisht Consulting, Inc. I reproduce that scatter plot here as Figure 15-1. Each point represents one employee’s ...

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