Outcomes of social care for adults: developing a preference-weighted measure

The aim of this study was to develop a measure of social care outcome, an equivalent to the quality-adjusted life year (QALY) in health, which could be used in a range of circumstances.

The project drew on previous and parallel work developing the Adult Social Care Outcome Toolkit and the national Adult Social Care Survey. We developed and tested an instrument designed to reflect service users' social care-related quality of life (SCRQoL) and tested it with 30 service users from a variety of user groups and 300 older home care service users. In parallel, we explored discrete choice experiment (DCE) and best-worst scaling (BWS) approaches to preference elicitation with 300 members of the general population, and cognitively tested these with service users. We also cognitively tested a computer-aided time trade-off (TTO) exercise using SCRQoL attributes with members of the general population. In the second phase, using the finalised instruments, BWS interviews were conducted with 500 members of the general population, TTO interviews with a follow-up sample of 126 of these respondents, and BWS interviews with 458 people using equipment services.

The final measure had eight domains: personal cleanliness and comfort, accommodation cleanliness and comfort, food and drink, safety, social participation and involvement, occupation, control over daily life and dignity. In addition to measuring current SCRQoL, the instrument includes questions used to establish service users' views of their 'expected' SCRQoL in the absence of services. The difference between a person's current and 'expected' SCRQoL provides an indicator of service impact.

There was good evidence for the validity of the descriptive system and the validity of the current, expected and SCRQoL gain scales. The DCE and BWS approaches yielded similar results and, once introductions made clear, were understood by service users. BWS was used for the main stages, as it had technical and cognitive advantages. The computer-aided approach to TTO worked well, and respondents found questions acceptable and understandable. There were no substantive differences in the preferences of service users and the general population. The key domain was control over daily life, with the lowest and highest levels strongly estimated in all models. After allowing for observable heterogeneity, service users' preferences appeared to be more closely associated with their own SCRQoL than with those of the general population. The consistency of the results with the results of a previous study allowed the final model to be based on the preferences of 1000 members of the general population. A formula based on the relationship between TTO and BWS values was estimated for a social care QALY, with '0' equivalent to 'being dead' and '1' being the 'ideal' SCRQoL state. Members of the population experienced significantly higher SCRQoL than service users.

Although further work is needed, particularly to develop an equivalent measure for informal carers and to explore the links with health QALYs, the measure has considerable potential. A number of methodological advances were achieved, including the first application of TTO in a social care context and use of BWS to establish service user preferences.

The National Institute for Health Research Health Technology Assessment programme.