Use the R code on this chapter’s Web page to generate data that could lie behind exercise 16.7 and then run the analysis of variance.

Exercise 16.7

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 problemsolving 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?

Transcribed Image Text:

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