What Has Been Demonstrated by Research Comparing the Effectiveness of Psychotherapists

What has been demonstrated by research comparing the effectiveness of psychotherapists who received training in a number of different areas (psychology, psychiatry, counselling, and social work) ?

A) Clinical psychologists tend to be more effective than psychiatrists.
B) No reliable association exists concerning therapists' professional training and effectiveness.
C) Psychiatrists tend to be more effective than clinical and counselling psychologists.
D) Psychologists and psychiatrists tend to be more effective than counsellors and social workers.