ARE RELATIONSHIPS BETWEEN SF-36 SUBSCALES AND HEALTH UTILITY MERELY LINEAR?
Andrew P. Yu, MA, MS, Yanni F. Yu, MA, and Michael B Nichol, PhD. University of Southern California, Pharmaceutical Economics and Policy, Los Angeles, CA Purpose: The underlying relationship between health status scales (e.g. SF-36 domains) and utility is unknown. Previous studies assumed SF-36 scales mapped linearly to utility measures. Such an assumption provides a simple algorithm, but may be inconsistent with derived power functions, and may yield poor model fitting, lower predictability and regression artifacts. This study was to examine the nonlinear relationships between SF-36 subscales and HUI2 utility. Methods: Data included 6923 Southern California Kaiser Permanente members who filled both SF-36 and HUI2 in year 1994-1995. Missing values were imputed on item level by MCMC and propensity score method with a missing at random assumption. In order to relax the assumption of linear effect SF-36 subscales on utility, we used restricted cubic spline functions (CSF) with four or fiv
