Foa, Rothbaum, Riggs, and Murdock (1991) conducted a study evaluating four different types of therapy for rape victims. The Stress inoculation therapy (SIT) group received instructions on coping with stress. The Prolonged exposure (PE) group went over the events in their minds repeatedly. The Supportive counseling (SC) group was taught a general problem-solving technique. Finally, the Waiting list (WL) control group received no therapy.

The data follow, where the dependent variable was the severity rating of a series of symptoms.

Group n Mean S.D.

SIT 14 11.07 3.95 PE 10 15.40 11.12 SC 11 18.09 7.13 WL 10 19.50 7.11

a. Run the analysis of variance, ignoring any problems with heterogeneity of variance, and draw whatever conclusions are warranted.

b. Apply Welch’s procedure for heterogeneous variances. Does this affect your conclusions?

c. Draw a graph showing the means of the four groups.

d. What does rejection of H0 mean in this case?