Estimation and comparison of derived preference scores from the SF-36 in lung transplant patients

The purpose of this study was to estimate and compare preference scores derived from MOS Short Form-36 (SF-36) data for a sample of lung transplant patients using three methodologies: Fryback et al. (Med Decis Making 1997; 17: 1-9), Nichol et al. (Med Decis Making 2001; 21: 105-112) and Brazier et al. (J Health Econ 2002: 21: 271-292). Data were gathered from 99 lung transplant recipients using a mail survey, which included the SF-36 and other health-related quality of life (HRQL) measures. The mean preference score for the sample was 0.643 (range 0.43-0.83), 0.765 (range 0.36-1.0), and 0.697 (range 0.33-1.00) for Fryback, Nichol and Brazier methods, respectively. Correlations between the derived scores and visual analogue ratings of health (0.58-0.68) and pulmonary symptoms (-0.59 to -0.62) were moderate to good and in the expected directions. The mean preferences of patients grouped by levels of dyspnea, depression symptoms, illness burden, and self-rated general health differed significantly with all methods and supported the construct validity of the derived scores as measures of preference. The Nichol and Brazier scores, both derived with standard gamble utilities, were generally higher than Fryback scores, which are not utility-based. Given the popularity of the SF-36, these three methods could be useful where direct elicitation of preferences is not feasible. Researchers must be cognizant of the derivation method used, as absolute preference levels, hence quality adjusted life years (QALYs), will differ by method.