Measuring barriers to adherence: validation of the problematic experiences of therapy scale

Purpose: To present the psychometric properties of the Problematic Experiences of Therapy Scale (the PETS), a brief measure to assess self-reported perceived barriers to adherence to physical rehabilitative therapy. Methods: Participants (study 1: n = 128, study 2: n = 227) taking part in trials of rehabilitative exercises completed the PETS and adherence questions at 12 weeks. Participants in study 2 were also asked about maintained adherence at 6-month follow-up. Results: Principal component analysis identified a four-factor structure relating to symptoms, uncertainty, doubts and practical problems. Cronbach's alphas ranged between 0.84 and 0.96 for study 1 and study 2. Correlations between factors varied, ranging between -0.22 and -0.53 for study 1, and 0.12 and 0.36 for study 2. Adherence was associated with all subscales at 12 weeks, and with the symptoms and doubts subscales at 6-months. Conclusions: The PETS is a valid and reliable measure that can be used to assess participants' perceived reasons for non-adherence to a home-based rehabilitative therapy. It can be easily incorporated into treatment trials and as subscales were associated with reported adherence and maintained adherence, it provides potentially valuable indicators of reported barriers to adherence or might be used in clinical practice to facilitate conversations about adherence.