Chapter 15

Correlation: The Rise and Fall of Relationships

IN THIS CHAPTER

Understanding what correlation is all about

Connecting correlation and 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 scores 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 graphical 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 total SAT scores.

image

FIGURE 15-1: A scatterplot of 20 students’ SATs and GPAs at Sahusket University.

Each point represents one student. A point’s location in the horizontal direction represents the student’s SAT. That same point’s location in the vertical direction represents the student’s GPA.

Understanding Correlation ...

Get Statistical Analysis with Excel For Dummies, 4th Edition now with the O’Reilly learning platform.

O’Reilly members experience books, live events, courses curated by job role, and more from O’Reilly and nearly 200 top publishers.