Abstract
BackgroundPatient reported outcome measures (PROMs) are widely used in mental healthcare research for quality of life assessment but most fail to capture the breadth of health and non-health domains that can be impacted. We report the psychometric validation of a novel, multi-dimensional instrument based on Amartya Sen’s capability approach intended for use as an outcome measure in mental health research.MethodsThe Oxford Capabilities Questionnaire for Mental Health (OxCAP-MH) is a 16-item self-complete capability measure that covers multiple domains of functioning and welfare. Data for validation of the instrument were collected through a national randomised controlled trial of community treatment orders for patients with psychosis. Complete OxCAP-MH data were available for 172 participants. Internal consistency was established with Cronbach’s alpha; an interclass correlation coefficient was used to assess test-retest reliability in a sub-sample (N = 50) tested one week apart. Construct validity was established by comparing OxCAP-MH total scores with established instruments of illness severity and functioning: EuroQol (EQ-5D), Brief Psychiatric Rating Scale (BPRS), Global Assessment of Functioning (GAF) and Objective Social Outcomes Index (SIX). Sensitivity was established by calculating standard error of measurement using distributional methods.ResultsThe OxCAP-MH showed good internal consistency (Cronbach’s alpha 0.79) and test-retest reliability (ICC = 0.86). Convergent validity was evidenced by strong correlations with the EQ-5D (VAS 0.52, p < .001) (Utility 0.45, p < .001), and divergent validity through more modest associations with the BPRS (−0.41, p < .001), GAF (0.24, p < .001) and SIX (0.12, p = ns). A change of 9.2 points on a 0–100 scale was found to be meaningful on statistical grounds.ConclusionsThe OxCAP-MH has demonstrable reliability and construct validity and represents a promising multi-dimensional alternative to existing patient-reported outcome measures for quality of life used in mental health research.
Highlights
Patient reported outcome measures (PROMs) are widely used in mental healthcare research for quality of life assessment but most fail to capture the breadth of health and non-health domains that can be impacted
Complete OxCAP-MH and other relevant outcome baseline data were available for 172 patients
This study reports the statistical evaluation of the psychometric properties of a multi-dimensional capability instrument designed for use in a mental health context
Summary
Patient reported outcome measures (PROMs) are widely used in mental healthcare research for quality of life assessment but most fail to capture the breadth of health and non-health domains that can be impacted. Many established PROMs focus on a narrow range of outcomes, and fail to capture the full range of health and non-health domains that can be impacted by an illness or intervention [9]. The EQ-5D has been criticised on methodological and conceptual grounds It focuses exclusively on health-related quality of life and fails to capture non-health benefits and broader welfare inequalities, and, second, it has been shown to lack sensitivity when applied to mental health populations, those with psychotic disorders and severe and complex non-psychotic disorders [9, 14]
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