Supplementary Material for: Internet-Based Self-Help for Trichotillomania: A Randomized Controlled Study Comparing Decoupling and Progressive Muscle Relaxation

Abstract

<b><i>Background:</i></b> Trichotillomania (TTM) is characterized by recurrent hair-pulling that results in substantial hair loss. A previous pilot study demonstrated that the online self-help intervention ‘decoupling' (DC) might be effective at reducing hair-pulling symptoms, with a stronger effect than progressive muscle relaxation (PMR). We aimed to extend these findings using a more robust randomized clinical trial design, including diagnostic interviews by phone, a 6-month follow-up and e-mail support. <b><i>Methods:</i></b> One hundred five adults with TTM were recruited online and randomly allocated to either DC (n = 55) or PMR (n = 50). The intervention lasted 4 weeks, with severity of TTM assessed at 3 time points (before intervention, immediately after intervention and at the 6-month follow-up) using the Massachusetts General Hospital Hair-Pulling Scale (MGH-HPS). Both intention-to-treat and completer analyses were conducted. <b><i>Results:</i></b> Intention-to-treat analysis demonstrated highly significant and comparable symptom reductions (MGH-HPS) in both the DC and PMR groups (p < 0.001, partial η² = 0.31) that persisted through 6 months of follow-up. Participants' subjective appraisals favoured DC in some areas (e.g. greater satisfaction with DC than PMR). Completer analyses demonstrated the same pattern as the intention-to-treat analyses. <b><i>Conclusions:</i></b> Despite subjective appraisals in favour of DC, symptom reduction was comparable in the two groups. While the results suggest that even short Internet-based interventions like DC and PMR potentially help individuals with TTM, a partial effect of unspecific factors, like regression towards the mean, cannot be ruled out. Therefore, longitudinal studies with non-treated controls are warranted