Operationalising the capability approach as an outcome measure in public health: The development of the OCAP-18

There is growing interest in operationalising the capability approach to measure quality of life. This paper reports the results of a research project undertaken in 2007 that sought to reduce and refine a longer survey in order to provide a summary measure of wellbeing and capability in the realm of public health. The reduction and refinement of the questionnaire took place across a number of stages, using both qualitative (five focus group discussions and 17 in-depth interviews) and quantitative (secondary data analysis, N = 1048 and primary data collection using postal surveys and interviews, N = 45) approaches. The questionnaire was reduced from its original 60+ questions to 24 questions (including demographic questions). Each of Nussbaum's ten Central Human Capabilities are measured using one (or more) of the 18 specific capability items which are included in the questionnaire (referred to as the OCAP-18). Analysis of the questionnaire responses (N = 198) found that respondents differed with respect to the levels of capabilities they reported, and that these capabilities appear to be sensitive to one's gender, age, income and deprivation decile. An index of capability, estimated by assuming equal weight for each capability question, found that the average level of capability amongst respondents was 12.44 (range 3-17.75). This index was found to be highly correlated with a measure of health (EQ-5D) and wellbeing (global QoL), although some differences were apparent. This project operationalised the capability approach to produce an instrument to measure the effectiveness (and cost effectiveness) of public health interventions; the resulting OCAP-18 appears to be responsive and measure something supplementary to health and wellbeing, thus offers a promising addition to the current suite of outcome measures that are available.