Therapy Outcome Studies Depend on Ratings of the Changes Seen

Therapy outcome studies depend on ratings of the changes seen in clients. One reason that therapists' ratings may be unreliable is because

A) they have a limited range of clients on whom to compare an individual client's improvement.
B) they usually base their judgments on superficial personality tests.
C) they are not in a good position to compare behavior before and after treatment.
D) they cannot see the client's behavior in a range of settings.