Mapping the Washington Group on Disability Statistics disability measure to the Health Utilities Index Mark 3: Development and validation of a predictive multivariable model in a general population sample.

Background: Statistics Canada routinely collects information on functional health and related concepts. Recently, the Washington Group on Disability Statistics (WG) measure of disability has been introduced to the Canadian Community Health Survey (CCHS). The WG measure is used as a tool for developing internationally comparable data on disability. In alternate cycles of the CCHS, it replaces the Health Utilities Index Mark 3 (HUI3), a generic preference-based measure of health-related quality of life. The HUI3 is used to derive evaluative health measures common in population health and economic evaluations. Since the WG measure is not preference-based, it is unable to derive these measures. To address resulting data gaps, this study empirically maps the health state utility values of the HUI3 score from the WG measure.

Data and methods: Empirical mapping used a "head-to-head" subsample of the 2017 CCHS where WG and HUI3 measures were collected from the same respondents aged 40 and over. Empirical mapping used regression models to estimate the statistical relationship between WG and HUI3 measures in addition to health and demographic variables. Out-of-sample predictive performance was assessed through descriptive statistics, mean absolute error, and other measures of predictive accuracy.

Results: The preferred estimation strategy resulted in reasonably precise estimates of the HUI3 score corresponding to trends across health and demographic characteristics and reflecting distributional properties of the HUI3 score. Inclusion of different components of the WG measure influenced predictive accuracy.

Interpretation: Empirical mapping offers a potential method to estimate health state utility scores from the WG measure and addresses data gaps in health-related quality of life measures in the CCHS when HUI3 is not collected.