Rasch analysis of a patient-reported outcome measure for self-perceived health among psychiatric patients in Denmark

Background Patient-reported outcome measures (PROMs) are valuable and necessary tools for establishing and maintaining patient-centred healthcare. The PRO-Psychiatry initiative was primarily initiated to support the patient’s voice in treatment decision-making and secondarily to monitor patient-perceived quality of care. The result of the initiative is a patient-reported instrument developed in collaboration between patients and clinicians. We aimed to validate the PROM developed for measuring self-perceived health among psychiatric patients in North Denmark Region, in terms of internal consistency, criterion validity and responsiveness. Method Patients in contact with a psychiatric hospital in the North Denmark Region from September 2018 to March 2021 were included in the study. The PROM constitutes a scale of 17 items covering various aspects of self-perceived health including well-being (7 items), lack of well-being (5 items) and social functioning (5 items), where the former domain entails the WHO-5 Well-Being Index. The potential range of the total scale score is 0–85. We applied McDonald’s omega, average inter-item correlation (AIIC) and differential item functioning (DIF). In addition, we used mixed effects analyses to estimate temporal correlations. The instrument was compared with self-rated overall mental and psychiatric health. Results The patient population consisted of 1132 unique patients and a total of 2476 responses corresponding to one response per patient pathway. McDonald’s omega was found to be 0.92 (95% CI 0.92 to 0.93), while the AIIC was found to be 0.42 (95% CI 0.39 to 0.44). For DIF, the largest systematic variation resulted in a maximum difference of 2.3 points on the total score when adjusting for the latent trait and was found when comparing initial measurements with follow-up measurements. The correlation between the total score and the outcomes regarding overall physical and mental health was 0.52 (95% CI 0.48 to 0.56) and 0.74 (95% CI 0.72 to 0.76). Similar correlations were found ...