Invariance and inconsistency in utility ratings

Purpose. To assess utilities of composite health states for dependence in activities of daily living (ADLs) for invariance (i.e., when subjects provide 0 utility of 1 for all health states) and order inconsistency (i.e., when subjects order their utilities such that their utility for a combination of ADL dependencies is greater than their utility for any Subset of the combination). Methods. Each of the 400 subjects, age 65 y and older, enrolled in one of several regional medical centers of the Kaiser Permanente Medical Care Program of Northern California and provided standard-gamble utilities for single ADL dependencies (e. a., bathing dressing, continence) and for dependence in 8 other combinations of ADL dependencies. For order-inconsistent responses, the authors Calculated the maximum magnitude of inconsistency as the maximum difference between the utility for the combined ADL dependence health state and that of its inconsistent subset. Results. A total of 76 subjects (19%) gave a utility of 1.0 for all health states presented to them; 19 (5%) gave the same utility other than 1.0 for all health states; 130 (33%)gave at least 1 utility < 1.0 and had no order inconsistencies; and 175 (44%) hod at least 1 order inconsistency. Invariance was associated with a Mini-Mental Status Examination score < 28.6 (P = 0.01), with education < 12 y (P = 0.004), with race/ethnicity other than non-Hispanic White/Caucasian (P = 0.001), and with shorter time spent on the utility elicitation task (P < 0.0001). Among the inconsistent subjects, 69% had a maximal magnitude of inconsistency that was within 1 standard deviation of the mean utilities. The maximal magnitude of inconsistency was associated with longer time spent on the elicitation task (P < 0.0001) and race/ethnicity other than non-Hispanic White/Caucasian (P = 0.005). The mean (s) utility for dependence in continence among consistent subjects who were not invariant (0.88 [0.24]) was higher than among inconsistent subjects (0.80 [0.27]; P = 0.01). Conclusions. Invariance and order inconsistencies in utility ratings for complex health states occur frequently. Utilities of consistent subjects may differ from those of inconsistent subjects. Utility assessments should attempt to measure and report these patterns.