DOUBLE-BLINDNESS PROCEDURES, RATER BLINDNESS, AND RATINGS OF OUTCOME - OBSERVATIONS FROM A CONTROLLED TRIAL

Background: We determined whether blindness in a double-blind randomiz ed controlled trial of alprazolam and exposure therapies in patients w ith panic disorder and agoraphobia was maintained in assessors and pat ients, what were the factors related to ''unblinding,'' and whether un blinding was associated with clinical outcome. Method: In 129 patients with panic disorder and agoraphobia who were randomized to alprazolam -exposure, placebo-exposure, alprazolam-relaxation, or placebo-relaxat ion conditions, blindness was tested at the end of treatment by the in dependent assessors' and patients' classification of the treatment con dition. Results: Assessors' classifications were correct in 82% of the alprazolam group and 78% of the placebo group; corresponding figures for patients' classifications were 73% and 70%, respectively. Factors associated with unblinding included drug side effects but not assessor s' ratings of treatment outcome. Conclusion: Judgment of the validity of the outcome of a randomized controlled trial is easier if the repor t notes not only the use of a double-blindness procedure but also deta ils how blind the raters remained and how any unblinding affected thei r ratings of clinical outcome.