Everitt reported data on a study of three treatments for anorexia in young girls. One treatment was cognitive behavior therapy, a second was a control condition with no therapy, and a third was a family therapy condition. These are the same data we examined in Chapter 14.

The data follow.

a. Run an analysis of variance on group differences in Gain scores. (You may have already done this in Chapter 14.)

b. Now run the analysis on Posttest scores, ignoring Pretest scores.

c. Finally, run the analysis on Posttest scores using Pretest as the covariate.

d. How do these three answers relate to one another, and what do they show about the differences and similarities between analysis of covariance and the treatment of gain (or change) scores?

e. Calculate h2 on Groups for the analysis of covariance.

f. Calculate d for the contrast on the two therapy groups (ignoring the control group)
using adjusted means.