Independent evaluator knowledge of treatment in a multicenter comparative treatment study of panic disorder

The purpose of this study was to examine independent evaluators' (IEs) blindness to treatment condition during a Multicenter Comparative Treatment Study of Panic Disorder. IEs were 15 doctoral- and masters-level clinicians in psychology, social work, and medicine. They conducted three post-treatment assessments with each patient. Immediately after each assessment interview, IEs completed a form indicating which of the five possible treatments they believed the patient had received and any specific information that provided IEs with information about a patient's treatment condition. These forms were completed for 170 patients. Analyses were conducted to determine the accuracy of guesses about treatment condition by IEs during post-treatment assessments, the relationship between accuracy of IE guessing and actual treatment assignment, the relationship between accurate guessing and outcome ratings, and contributors to the breaking of the blind. A significant relationship was found between IE guesses and actual treatment at all three assessment points, across individual IEs, treatment sites, and IE professional affiliations. IEs were no more accurate in their guessing about patients taking medication than those receiving behavior therapy. Patients and project staff inadvertently provided information to IEs that enhanced the rates of accurate guessing. Implications of these findings on interpretation of the treatment study are discussed, and recommendations are made for improving blindness procedures.