Development of a self-report measure of capability wellbeing for adults: the ICECAP-A

This paper has described the development of a brief, capability wellbeing measure for the general adult population. The measure aims to capture individuals’ freedom to function in five key areas of their life, identified through in-depth interviews. Informants were sampled specifically to ensure wide representation and thus applicability of the final set of capabilities (and the wording). In contrast to much previous work to develop outcome measures for economic evaluation [27] (although in common with some recent studies [20, 28, 29]), qualitative methods have been used. This approach grounds the attributes in the values and terminology of the general population and ensures that a limited set of items can be generated to cover a broad range of concepts.

This study suggests a similar, yet not identical, list of attributes for adults in general to that for older adults [20]. The attributes of “attachment”, “autonomy” and “enjoyment” are almost identical, albeit with some adjustment in wording, to three attributes in the ICECAP-O measure. The main differences for the ICECAP-A measure were in the “stability” and “achievement” attributes. “Stability” bears a strong similarity to the “security” attribute in ICECAP-O; however, the emphasis on “stability” is on the present (in terms of current feelings of comfort and continuity), as well as the future. Similarly, the “achievement” attribute in ICECAP-A goes beyond the “role” attribute in ICECAP-O, encompassing progressing and excelling in life, concepts that may not stem from having a role. In Nussbaum’s list of central human capabilities [18], there are three capabilities (“emotions”, “control” and “play”), which are close equivalents to the “attachment”, “autonomy” and “enjoyment” capabilities found in this study. Whilst there are no direct equivalents for “achievement” and “stability”, these issues are also touched on in Nussbaum’s list (e.g. Nussbaum’s concern for security against assault is likely to come into “feeling settled and secure”). The ICECAP-A attributes are also broadly similar to those proposed in the non-capabilities-based wellbeing literature. For example, the ICECAP-A attributes of “attachment” and “autonomy” in ICECAP-A are not dissimilar to Ryff’s [12] theory-derived dimensions of “positive relations with others” and “autonomy”. Ryff’s dimensions of “purpose in life” and “personal growth” are similar to “achievement” in ICECAP-A, whilst “self-acceptance” has links to “stability”.

The measures that are used in economic evaluation to generate QALYs typically focus on health-related quality of life. These tend to go beyond a strict biomedical definition of health [30], but there is no consensus on what exactly should be measured. Current measures, such as the EQ-5D [31] incorporate attributes right across the health spectrum, from specific impairments (pain) and disabilities (mobility) to the impact of poor health on participation in life (usual activities). This raises the concern that health effects may be double counted [27]. Furthermore, health-related quality of life measures focus on selected aspects of participation in life; for example, the AQOL [32] directly considers the impact of poor health on relationships, whilst the EQ-5D does not. Full use of the capability approach in health economics entails going beyond health to consider an individual’s wellbeing in a broader sense [33]. Focusing on what an individual can be and do in their life does not (conceptually at least) limit the possible ways in which healthcare interventions can impact on an individual’s life. Arguably, by treating health as an influence, it is also less susceptible to double counting both the impairment that health problems cause and the impact that this impairment has on an individual’s life.

In developing the measure, the ability to live in a good or “just” world was important to some respondents. However, it was rejected as a potential attribute for two reasons. First, such a capability is unlikely to be informative when evaluating the benefits of, for example, a new drug or surgical device in a UK context. Second, ‘living in a just world’ might be ‘too important’, in that by dominating all other attributes it cannot be quantitatively valued using proposed econometric techniques [34].

A key strength in the work is that it drew on both the capability approach and mainstream health economics approach to outcome development. This involved placing an emphasis on public participation in developing the content of the measure [19, 35] but with an end goal of generating a concise outcome measure that can be valued using econometric techniques to obtain a single index value [27]. Furthermore, the iterative nature of the interviews helped ensure face validity and provide information as to respondents’ understanding of the terminology in an efficient manner.

Limitations to the work also need to be discussed. Although a diverse sample of informants was recruited, the three informants that were recruited through snowball sampling were friends of one informant and therefore there may have been less variation in the views of the younger age group in the sample. Furthermore, the sampling strategy excluded those individuals who were not on the electoral register, which will have meant that some individuals on the margins in society (in prisons and institutional care, for example) will have been excluded, as well as those who opted not to be on the electoral register. In common with other qualitative studies, one cannot be sure that different researchers would not come up with different attributes. However, the influence of a single researcher was minimised by the checking of findings with the broader research team and with informants themselves. In general, further testing of the measure’s reliability and validity will be important if it is to be a credible outcome measure for use in trials and economic evaluations. Preliminary work is underway to use tests of association with socio-economic variables [36] to explore construct validity and think-aloud interviews [25] to explore the completion processes for the measure. The latter will allow further investigation of the degree to which individuals think about their freedoms in life (rather than simply their functionings) when they respond to the questions. Finally, one concern is that because the measure focuses on an individual’s capability wellbeing in broader sense, the measure will be less sensitive than measures of generic health. This clearly merits consideration, but it is an issue that can only be explored through using the measure in a variety of health and social care settings.

In conclusion, this work has generated a measure to assess health and social care interventions in terms of their impact on an individual’s “capability to do and be the things that are deemed valuable in their life”. Further research will be conducted to generate index values for use with the measure using best-worst scaling [37]. Work is also required to further assess the acceptability and appropriate application of the approach; such work could proceed through interviews with potential users of the measure and healthcare decision-makers. Potentially, however, the ICECAP-A measure provides a useful step forward in the development of measures of broader wellbeing for comparing the effectiveness and cost-effectiveness of the increasingly diverse array of health and social care interventions.