Research on Family Systems Theories and Therapies Is Difficult to Do

Research on family systems theories and therapies is difficult to do because:

A) it involves observing people in the context of their relationships, which is difficult to "capture in the laboratory."
B) it often does not receive adequate funding for research as it is not recognized as a formal therapeutic approach.
C) it is a relatively new therapeutic approach and very few professionals have expertise in this area.
D) families are always in a state of flux and findings may lack validity and reliability.