Measurement properties of the Comprehensive Quality-of-Life Measure for Acne (CompAQ): a cohort study at three international sites

Abstract Background The Comprehensive Quality-of-Life Measure for Acne (CompAQ) is a patient-reported outcome measure (PROM) assessing health-related quality of life (HRQoL) among patients with acne. The measure is one of two acne-specific PROMs that had the strongest evidence to support its use in a recent COSMIN systematic review. Objectives To build on prior validation studies of CompAQ by confirming several of its known measurement properties in a cohort of patients with acne at three international sites; and, to establish the responsiveness of the measure during acne treatment. Methods Adults being seen for routine acne treatment at dermatology clinics in Canada, the USA and Singapore were recruited between July 2022 and September 2024 to participate in this cohort study. At each visit, participants completed the CompAQ, which consists of 20 items representing five domains (i.e. emotions, social judgement, social interaction, treatment and symptoms domains) and several other relevant measures. Structural validity was assessed by confirmatory factor analysis, internal consistency by calculating Cronbach’s α values, and construct validity by known groups and convergent validity hypothesis testing. We further evaluated for differential item functioning (DIF) across study site, sex and age. In addition, we assessed responsiveness by change-score validity hypothesis testing and calculating standardized response means (SRMs). Results Our study included 315 participants [mean (SD) age 25.2 (6.1) years; 219 (69.7%) women] and data were collected from a total of 588 visits. The CompAQ was found to have sufficient structural validity, internal consistency and construct validity among patients at each study site and in the combined cohort. In addition, no statistically significant uniform or nonuniform DIF was flagged for most items when analysing DIF by site, sex and age. Based on SRM estimates, the emotions (SRM 0.927) and symptoms (0.914) domains had the largest responsiveness, while the social judgement (0.606), social interaction (0.522) and treatment (0.787) domains had more moderate responsiveness. Conclusions CompAQ represents a useful and responsive PROM to evaluate HRQoL among those with acne in clinical trials and clinical practice. Future studies are needed to evaluate the interpretability of the measure (i.e. identifying severity strata and minimally important differences).