A Longitudinal Comparison of 5 Preference-Weighted Health State Classification Systems in Persons with Intervertebral Disk Herniation

Objective. To assess the longitudinal validity of widely used preference-weighted measurement systems for economic studies of intervertebral disk herniation (IDH). Methods. Using data at baseline and 1 year from 1000 Spine Patient Outcomes Research Trial (SPORT) participants with IDH and complete data, the authors considered the EQ-5D with UK and US values (EQ-5D-UK and EQ-5D-US), 2 versions of the Health Utilities Index (HUI3 and HUI2), the SF-6D, and a regression-estimated quality of well-being score (eQWB). Differences in mean change scores (MCS) were assessed using signed rank tests, and Spearman correlations were calculated for change scores by system pairs. Using the Oswestry Disability Index, symptom satisfaction, progress rating, and self-perceived health ratings as criterion measures, the authors tested for trend in MCS across levels of change in criteria. They calculated floor and ceiling effects, effect size (ES), standardized response mean, and minimal important difference estimates. Results. All systems demonstrated linear trends with external criteria and moderate to strong correlations between systems. However, differences in performance were evident. SF-6D and eQWB were most responsive (ES: 1.9 and 2.3, respectively), whereas EQ-5D-US and EQ-5D-UK were least responsive (ES: 1.23/1.20). Ceiling and floor effects were noted for all systems within key dimensions and for EQ-5D-UK and EQ-5D-US for overall score. MCS ranged from 0.40 (0.38) for EQ-5D-UK to 0.13 (0.09) for eQWB and differed significantly, except between EQ-5D-US and HUI2. Conclusions. This research supports the validity of all systems for measuring change in persons with IDH, without finding a clearly superior system. The unique characteristics of each system revealed in this study should guide system choice.