VALUE MEASUREMENT IN COST-UTILITY ANALYSIS - EXPLAINING THE DISCREPANCY BETWEEN RATING-SCALE AND PERSON TRADE-OFF ELICITATIONS

Previous studies have shown a discrepancy between common utility elici tation methods, such as rating scale (RS) elicitations, and person tra de-off (PTO) elicitations. This discrepancy has generally been felt to be due to the fact that RS elicitations ask people to compare conditi ons to each other in terms of numbers on a visual rating scale, while PTO elicitations ask people to think in terms of numbers of people nee ding to be treated. However, there are three other cognitive differenc es between PTO and RS elicitations that might contribute to the discre pancy: In PTO elicitations, as opposed to RS elicitations: (1) people are asked to think about how conditions affect people other than thems elves; (2) people are asked to think about the benefit of treating con ditions; and (3) people are asked to chose who to treat among patients with different conditions. In this study, we attempt to determine whe ther any of these three cognitive differences contribute to the discre pancy between RS and PTO utility elicitations. We randomized prospecti ve jurors to receive one of several survey versions in which we manipu lated the RS and PTO elicitations to reduce the differences between th em, while preserving their underlying structure. In the RS-self survey , we asked subjects to rate a health condition on a scale from 0 to 10 0 as if they had the condition. In the RS-other survey, we asked peopl e to rate the health condition as if someone else had it. In the RS-cu re survey, we asked subjects to rate the benefits of curing someone el se of the health condition. In the PTO-comparison survey, we asked peo ple to determine equivalent numbers of people needing to be cured of t wo conditions in order to produce equal benefits. In the PTO-choice su rvey, we presented people with a budget constraint and asked them to d etermine equivalent numbers of people needing to be cured of two condi tions to help decide which group should be treated within the budget c onstraint. Two hundred and twenty two subjects completed surveys. Medi an utilities for health conditions were higher in the two PTO elicitat ions than in the three RS elicitations. There were no differences in u tilities across the two PTO surveys, nor across the three RS surveys. In addition, the PTO elicitations allowed people to make finer distinc tions among non-life threatening conditions than did the RS elicitatio ns. The discrepancy between RS and PTO elicitations cannot be explaine d by shifting subjects attentions from themselves to others, nor from conditions to the benefit of treating conditions. Instead, the discrep ancy occurs because of the general format of RS and PTO elicitations. (C) 1998 Published by Elsevier Science Ireland Ltd.