A study found that patients referred by their doctors to psychotherapists practicing a new experimental form of therapy made more progress with respect to their problems than those referred to psychotherapists practicing traditional forms of therapy
Therapists practicing the new form of therapy, ttherefore, are more effective than therapists practicing traditional forms
It ignores the possibility that the patients referred to therapists practicing the new form of therapy had problems more amenable to treatment than did those referred to therapists practicing traditional forms.