Chapter 13
Correlation: The Rise and Fall of Relationships
IN THIS CHAPTER
Understanding what correlation is all about
Connecting correlation with regression
Analyzing correlation in R
In Chapter 12, I introduce 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, a regression-related tool for looking at relationships.
I use the example of employee aptitude and performance from Chapter 12 and show how to think about the data in a slightly different way. I also show you how to test hypotheses about relationships and how to use R functions for correlation.
Understanding Correlation
Correlation is a statistical way of looking at a relationship. When two things are correlated, it means that they vary together. Positive correlation means that high scores on one are associated with high scores on the other, and that low scores on one are associated with low scores on the other as in the Aptitude-Performance example in Chapter 12.
Negative correlation, on the other hand, means that high scores on the first thing are associated with low scores on the second. Negative correlation ...