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 for the corresponding changes over time.

CONCLUSION: The scale showed high consistency and little systematic variation between the comparison groups. The concurrent correlations and analyses of responsiveness coincided with the prespecified hypotheses. Overall, we deem the Danish PRO-Psychiatry instrument to possess suitable psychometric properties for measuring self-perceived health among a psychiatric population.