A Researcher Compares 80 People Who Join Alcoholics Anonymous (AA)

Multiple Choice

A researcher compares 80 people who join Alcoholics Anonymous (AA) with 80 people who decide not to join. On the average, those in the AA group and those in the non-AA group have equal alcohol problems at the start. One year later, on the average, those in the AA group are healthier and are drinking less than those in the non-AA group. What is wrong with this study that prevents us from evaluating the effectiveness of the AA procedure?

A) lack of an independent variable
B) lack of a dependent variable
C) lack of random assignment to groups
D) lack of demand characteristics