Measuring broader wellbeing in mental health services: validity of the German language OxCAP-MH capability instrument

The OxCAP-MH capabilities questionnaire was developed and validated in the UK for outcome measurement in mental health clinical studies. Its broader wellbeing construct or validity in routine mental health services so far has not been assessed. The objectives were to investigate the extent the OxCAP-MH measures broader wellbeing compared to the EQ-5D-5L and to test psychometric properties of the German language OxCAP-MH in routine mental health services in Austria.

Study sample consisted of patients in socio-psychiatric services (n = 159) assessed at baseline and 6-month follow-up. Underlying factors associated with quality-of-life/wellbeing concepts measured by the OxCAP-MH and EQ-5D-5L were identified in exploratory factor analysis (EFA). Responsiveness was assessed using anchor questionnaires and standardised response mean (SRM). For discriminant validity, subgroups of respondents were compared using t test and one-way ANOVA. Test-retest analysis was assessed for a period of maximum 30 days from the baseline assessment with intra-class correlation coefficient (ICC).

EFA identified a two-factor structure. All EQ-5D-5L items and seven OxCAP-MH items loaded on one factor and nine remaining OxCAP-MH items loaded on a separate factor. Responsiveness was found for patients who improved in anchor questionnaire scores with large or moderate SRM statistics. OxCAP-MH discriminated between various groups in univariable and multivariable analyses. Reliability of the German language OxCAP-MH was confirmed by ICC of 0.80.

Besides providing evidence that the OxCAP-MH measures broader wellbeing constructs beyond traditional health-related quality of life, the study also confirms the validity of the instrument for implementation in routine evaluation of mental health services.