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. Those in the Supportive Counseling (SC) group were taught a general problem solving technique. Finally, the Waiting List (WL) control group received no therapy. Data with the same characteristics as theirs follow, where the dependent variable was the severity rating of a series of symptoms.

(a) Run the analysis of variance, ignoring any problems with heterogeneity of variance, and draw whatever conclusions are warranted. (Note that you have to be a little creative here, but it is not a difficult exercise.)
(b) Draw a graph showing the means of the four groups.
(c) What does rejection of the null hypothesis mean?

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Group Mean S.D. SIT PE SC WL 11.07 15.40 8.09 9.50 3.95 11.12 7.13 7.11 14 I0 10