A new paradigm to evaluate quality-adjusted life years (QALY) from secondary database: Transforming health status instrument scores to health preference

Assessing Health Related Quality of Life (HRQOL) through generic health status instruments has gained considerable attention in today's clinical practices. Nevertheless, one of the drawbacks of the generic HRQOL instruments (SF-36, SF-12 etc.) is that these are unsuitable for direct estimation of health preference that can then be used to generate Quality Adjusted Life Years (QALY). QALY is a useful outcome measure that reflects both life expectancy and quality of life and is suitable for cost-effectiveness or cost-utility analyses. Objective. To estimate a summary health utility index (represented by the Health Utility Index (HUI) and Linear Analog Scale (LAS)) from the domains of the SF-36, and items of the SF 12. Methods. Data were collected from a longitudinal survey (three administrations) of a large cross-section of patients under managed care. The SF-36 was used to assess health status and the LAS and HUI were used to assess health state preference. The SF-12 items were also created from the SF-36 by using a published algorithm. The SF-36 and the LAS were administered at baseline, year 1 and year 2, but the HUI was administered only in the last cycle. A linear regression model was used to predict HUI at year 2 from the SF-36 domains at year 2 along with socioeconomic and disease covariates. The predictive power of the SF 12 to estimate the HUI was tested using similar methods. A cross-sectional time series model was developed to estimate LAS from the SF-36 domains. Results. The SF-36 domains along with age and gender significantly accounted for 33% to 50% variations in HUI score depending on the model used. Additionally, the SF-36 domains were accounted for 47% variation in LAS scale score. The SF-12 items explained 46% variation in HUI score. Conclusion . This research provides substantial evidence that health state utility and QALYs can be estimated from secondary databases, which include the SF-36 or the SF-12.