Capability as an outcome measure in randomised controlled trials

‘The capability approach is a broad, normative framework for the evaluation of well-being’(p.94)[1], which has attracted growing interest in health and health economics research. A broader measure of well-being may more accurately capture the effects of some interventions, than traditional health-related quality of life measures. The ICECAP-A and ICECAP-O are two measures of a person’s well-being, with a theoretical grounding in the capability approach, designed for use in health and social care research. This thesis reports qualitative and quantitative investigations into the validity and responsiveness of the ICECAP measures. A methodological review of existing validation studies was completed. Seventeen semi-structured interviews with health research professionals were carried out and an iterative, constant comparative, thematic analysis was completed to assess the content validity of the ICECAP-A. The construct validity and responsiveness of the measures were assessed using two randomised controlled trials: the BEEP trial (ISRCTN 93634563) and the Past BP trial (ISRCTN 29062286). Qualitative and quantitative results provide positive indications of validity. The qualitative work showed that research professionals viewed the ICECAP-A as a relevant and feasible measure for use in health research. The quantitative results confirmed the majority of a priori hypotheses in the validity analyses, while longitudinal data provided evidence that the measures are responsive to self-reported changes in health status. In conclusion, this thesis reports the first assessment of validity in a randomised controlled trial setting and the first analysis of responsiveness. While further testing of the ICECAP measures is required, results indicate that the measures are appropriate for use in health research