Construct validity, reliability and responsiveness of the 10-item Well-being instrument (WiX) for use in economic evaluation studies

Objectives Economic evaluations of interventions in health and social care require outcome measures that capture their full benefits, including those beyond health. The aim of this study was to assess construct validity, test-retest reliability, and responsiveness of the newly developed 10-item Well-being instrument (WiX). Methods Data was gathered via an online survey in a representative sample of the adult general population in the Netherlands (N=1,045). Construct validity was assessed by inspecting convergent, structural and discriminant validity, following the COSMIN methodology. Regression analyses of the WiX and its items on other validated measures of well-being were performed to assess the convergent validity of the instrument and the relevance of its items. Dimensionality of the WiX was assessed using exploratory factor analysis. To assess discriminant validity, several hypotheses in terms of well-being differences were assessed. Finally, a second survey was sent out two weeks after the initial survey (N=563; 53.9% response rate) to assess the test-retest reliability and responsiveness of the WiX. Results The WiX showed to be correlated with alternative well-being measures as expected and able to sufficiently differentiate between relevant subgroups in the population. Moreover, the dimensionality analysis indicated that the WiX captures a broad array of elements relevant to well-being, including physical and mental health. The test-retest reliability was good, with an intraclass correlation coefficient of 0.82. Conclusions The results regarding the WiX are favourable and indicate that this new instrument may be a promising alternative for existing measures of well-being for evaluating interventions in health and social care.