Valuing health benefits : the development of a preference-based measure of health for use in the economic evaluation of health care from the SF-36 health survey
The main aim of the research was to develop a preference-based measure of health from the Short Form-36 (SF-36) Health Survey for valuing health-related quality of life on a 0 to 1 scale in order to calculate Quality adjusted life years (QALYs). Before undertaking the empirical work, reviews were undertaken of the justification for the QALY approach, existing preference-based measures for deriving QALYs and the rationale for looking at the SF-36. The methods of the research were as follows. The SF-36 was reduced and simplified to form a six dimensional health state classification (SF-6D) amenable to valuation. One hundred and sixty five patients, health professionals, managers, and students valued a sample of health states defined by the SF-6D using the visual analogue scale (VAS) and standard gamble (SG) techniques to elicit preferences. There were 1,357 VAS and 1,037 SG health state valuations after adjustment and exclusions for major inconsistencies. Models for predicting median and mean VAS and SG health state values from the SF-6D were estimated from these data by multivariate techniques. A set of additive models were selected on the basis of goodness of fit and parsimony. More complex specifications did not improve the models. Initial applications of algorithms based on these models to five data sets suggested this new preference-based measure retained much of sensitivity of the SF-36 at the milder end of the of the illness spectrum. The preference-based algorithms can be used to transform SF-36 data collected in a clinical trial (with costs) into information suitable for assessing the cost-effectiveness of health care interventions. The adoption of these algorithms has the potential to considerably extend the application of economic evaluation in health care.