PP2 - Are Time Trade-Off Values of Worse-Than-Death Health States Valid?

Abstract

To evaluate the validity of worse-than-death (WTD) values relative to better-than-death (BTD) values in 5-level EQ-5D value set studies from Singapore and the Netherlands. Health states were valued using the composite time trade-off (cTTO) method. Mean values were calculated for the severity distance from the full health (i.e., the sum of severity levels of given health-state minus 5) to examine correlation between utility value and severity. A linear mixed model (LMM) using 20 descriptor variables for severity levels in the five dimensions was fitted for utility values to examine the effect on health dimensions on utility value. The analyses were performed separately for BTD and WTD values. In Singapore (N=1000; proportion of WTD values: 32.6%), the mean of BTD values decreased from 0.89 to 0.21, whereas the mean of WTD values increased from -0.98 to -0.89 with increase in severity distance. Coefficients of the LMM based on BTD values ranged from -0.04 to -0.19 and were monotonic within each dimension with the exception between levels 4 and 5 for mobility and usual activities (Pseudo-R2 = 0.389). In contrast, 7 of the 20 coefficients (range: 0.027 to -0.034) of the model based on WTD values were positive; coefficients for only self-care and pain/discomfort were completely monotonic (Pseudo-R2 = 0.002). Results using the dataset from the Netherlands were similar to those from Singapore. WTD values are poorly associated with severity of health states, suggesting sub-optimal validity of the cTTO method for valuation of WTD EQ-5D health states.