"As this sample demonstrates, there are substantial differences in therapists’ performance. Fortunately, most therapists produce results comparable to what we would expect from well-conducted clinical trials, which is an effect size of approximately d= .80. About 25% have results that exceed this benchmark by 10% or more (d => .90), while about 25% will fall short by a similar amount (d < .68)". Are You Any Good…as a Therapist? | Society for the Advancement of Psychotherapy.