A Study Is Conducted to Determine the Effectiveness of Group

Multiple Choice

A study is conducted to determine the effectiveness of group therapy on abstinence among older people who are substance abusers. The older people involved in the study either receive group therapy or they are in a comparison group. The presence of a comparison group suggests

A) older people were randomly assigned to one of the two groups (group therapy or comparison)
B) older people were not randomly assigned to one of the two groups (group therapy or comparison)
C) the two groups are equivalent on all important characteristics
D) all alternative explanations can be ruled
E) the two groups were matched on important characteristics