Degree Name

Master of Arts (MA)

Semester of Degree Completion


Thesis Director

Charles Blaich


This thesis is a review of the validity of studies on the effectiveness of psychotherapy. Ten randomly selected studies are examined to determine if the validity of the study was affected by threats to statistical conclusion, internal, construct, and external validity. All of the studies examined were published after 1985. The results indicate that validity of the research on the effectiveness of psychotherapy is affected by some threats to validity: History, Testing, and Selection bias, (ie. internal validity). In addition, external validity was affected by the lack of use of appropriate control group, lack of a description of the therapy used and the condition under which it was used, and a lack of a description of placebo group used. The evidence from this thesis suggests a need for improvement in the design of efficacy studies. In addition, the evidence suggests the need for better data reporting so that the research can be replicated.