Chapter 10

Correlation and Regression

IN THIS CHAPTER

Bullet Exploring statistical relationships between numerical variables

Bullet Distinguishing between association, correlation, and causation

Bullet Making predictions based on known relationships

In this chapter, you analyze two numerical variables, X and Y, to look for patterns, find the correlation, and make predictions about Y from X, if appropriate, using simple linear regression.

Picturing the Relationship with a Scatterplot

A fair amount of research supports the claim that the frequency of cricket chirps is related to temperature. And this relationship is actually used at times to predict the temperature using the number of times the crickets chirp per 15 seconds. To illustrate, I’ve taken a subset of some of the data that’s been collected on this; you can see it in Table 10-1.

TABLE 10-1 Cricket Chirps and Temperature Data (Excerpt)

Number of Chirps (in 15 Seconds)

Temperature (Fahrenheit)

18

57

20

60

21

64

23

65

27

68

30

71

34

74

39

77

Notice that each observation is composed of two variables that are tied together, in this case the number of times the cricket chirped in 15 seconds (the X-variable), and the temperature ...

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