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BACKGROUND: 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. 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. METHODS: The 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. RESULTS: The 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. CONCLUSIONS: The 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.

Original publication

DOI

10.1186/s12955-017-0825-3

Type

Journal article

Journal

Health Qual Life Outcomes

Publication Date

28/12/2017

Volume

15

Keywords

Capabilities, Community treatment orders, Mental health, Outcome measurement, Psychiatry, Psychometric validation, Psychosis, Adult, Female, Health Services Research, Humans, Male, Mental Disorders, Mental Health Services, Middle Aged, Outcome Assessment (Health Care), Patient Reported Outcome Measures, Psychiatric Status Rating Scales, Psychometrics, Quality of Life, Reproducibility of Results