Meta-analysis of therapist effects in psychotherapy outcome studies Psychotherapy Research Crits-Christoph, P., Baronackie, K., Kurcias, J.S., Beck, A.T., Carroll, K., Perry, K., Luborsky, L, McLellan, A.T., Woody, G.E., Thompson, L., Gallagher, D., & Zitrin, C. 1991; 1 (2): 81-91