The previous chapter looked at comparing populations to see if there is a difference between the two. That involved two random variables that are similar measures. This chapter will look at two random variables that are not similar measures, and see if there is a relationship between the two variables. To do this, you look at regression, which finds the linear relationship, and correlation, which measures the strength of a linear relationship.
There are many other types of relationships besides linear that can be found for the data. This book will only explore linear, but realize that there are other relationships that can be used to describe data.