Psychosocial "Clubs" or "Clubhouses" for Patients with Schizophrenia Have Been

Psychosocial "clubs" or "clubhouses" for patients with schizophrenia have been formed as a part of some rehabilitation programs. Research indicates that participation in these clubs may help prevent relapses. However, it is difficult to interpret the improvement in these patients because

A) some patients are on medication and some aren't.
B) only the most psychotic patients participate.
C) patients who participate may be significantly different from those who don't.
D) a significant number of patients drop out before completing the program.