Wampold's Meta-Analytic Studies of Psychotherapy Led Him to Conclude That

Wampold's meta-analytic studies of psychotherapy led him to conclude that the differential superiority of one psychotherapy over another is misleading for each of the following reasons EXCEPT:

A) lack of client feedback about outcome during treatment.
B) overestimation of particular treatment effects by ignoring therapist effects.
C) lack of quivalence of comparative therapies in most randomized controlled trials.
D) researcher allegiance effects are sufficiently large to account from differences among specific treatment approaches.