“…There is considerable evidence that therapist effects are reduced in controlled clinical trials relative to naturalistic studies of clinical practice , presumably in part as a result of the greater training and supervision provided, as well as initial selection of talented therapists. This is not to say that all types of therapies require trained and experienced practitioners to produce maximum effect, but there is evidence that this is true for at least some types of interventions and for some populations (e.g., Burns & Nolen-Hoeksema, 1992 ;Lyons & Woods, 1991 ;Weisz, Weiss, Han, Granger, & Morton, 1995 ).…”