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One strategy to evaluate the effectiveness of psychotherapy is to compare people who enter psychotherapy with a matched control group of people who do not receive psychotherapy. When researchers combine and summarize the results of studies using this strategy, what overall conclusions emerge?

A. People in the psychotherapy group improve at about the same rate as the people in the untreated group.
B. People in the psychotherapy group actually improve at a slower rate than the people in the untreated group.
C. The people in the untreated group do not get better, while about a third of the people in the psychotherapy group get better, about a third deteriorate, and about a third remain unchanged.
D. Those not undergoing therapy often improve, but those undergoing therapy are more likely to improve and to improve more quickly with less risk of relapse.