Psychometric Properties of the Instrument for Scoring Clinical Outcomes of Research for Epidermolysis Bullosa patient score (iscorEB-p): a patient-reported outcome measure

Background In contrast to clinical diagnosis via external examination, patient-related outcome measures (PROMs) allow access to patients' internal perceptions. In the case of epidermolysis bullosa (EB) - a rare disease characterized by a wide variety of symptoms and individual disease courses - it is important to integrate the patient's perspective into diagnostic processes. The Instrument for Scoring Clinical Outcomes of Research for EB (iscorEB) is an EB-specific measurement tool, combining a clinician score (iscorEB-c) and a patient questionnaire (iscorEB-p). Objectives The aim of this study is to establish the iscorEB-p as an independent PROM tool by exploring its psychometric properties. Methods Sample-based psychometric testing and evaluation were performed on data collected via a multinational online cross-sectional study. Results Data analysis was performed with n = 95 participants across all EB types. The reliability and internal consistency of the iscorEB-p was excellent (alpha = 0.90). Principal component analysis with a varimax rotation resulted in a two-factor solution, explaining 55.6% of the total variance, with the distinct factors 'everyday life functioning' and 'specific EB symptoms'. Convergent validity was shown by high correlations to the Satisfaction With Life Scale (r = -0.52, P < 0.001), the Quality of Life in Epidermolysis Bullosa questionnaire (r = 0.72, P < 0.001) and the Epidermolysis Bullosa Family Burden of Disease questionnaire (r = -0.73, P < 0.001). Conclusions The iscorEB-p is a reliable and valid instrument to assess patient-reported health status of people with EB.