Validating indicators of treatment response: application to trichotillomania.

Different studies of the treatment of trichotillomania (TTM) have used varying standards to determine the proportion of patients who obtain clinically meaningful benefits, but there is little information on the similarity of results yielded by these methods or on their comparative validity. Data from a stepped-care (Step 1: Web-based self-help; Step 2: Individual behavior therapy; N = 60) treatment study of TTM were used to evaluate 7 potential standards: complete abstinence, ≥ 25% symptom reduction, recovery of normal functioning, and clinical significance (recovery + statistically reliable change), each of the last 3 being measured by self-report (Massachusetts General Hospital Hairpulling Scale; MGH-HPS) or interview (Psychiatric Institute Trichotillomania Scale). Depending on the metric, response rates ranged from 25 to 68%. All standards were significantly associated with one another, though less strongly for the 25% symptom reduction metrics. Concurrent (with deciding to enter Step 2 treatment) and predictive (with 3-month follow-up treatment satisfaction, TTM-related impairment, quality of life, and diagnosis) validity results were variable but generally strongest for clinical significance as measured via self-report. Routine reporting of the proportion of patients who make clinically significant improvement on the MGH-HPS, supplemented by data on complete abstinence, would bolster the interpretability of TTM treatment outcome findings.