In Exercise 7.25, we saw data from Everitt that showed that girls receiving cognitive behavior therapy gained weight over the course of that therapy. However, it is possible that they just gained weight because they got older. One way to control for this is to look at the amount of weight gained by the cognitive therapy group (n 5 29) in contrast with the amount gained by girls in a Control group (n 5 26), who received no therapy. The data on weight gain for the two groups is shown below.