Types of inconsistency in health-state utility judgments

In making judgments of health-related quality of life, respondents often compare the relative magnitude of two intervals between health states, such as the interval between normal health and blindness compared to that between normal health and death. We examined two ways of comparing such intervals: person-trade-off (PTO)-in which the judgment concerns matching numbers of people so that two changes are equivalent-and direct judgment of the ratio. Both measures showed ratio inconsistency (a ratio that should be the product of two other ratios is too high) and superadditivity (two ratios that should add to I are too high). Some responses in both methods implied that two intervals which should have been different (because they shared a top or bottom point, but differed on the other point) were nevertheless viewed by subjects as being of equal size. These equality responses were more common when death was the bottom (worse end) of both intervals being compared (e.g., the interval between death and blindness is perceived as being the same size as the interval between death and normal health) than when any other condition was at the bottom or when the condition common to the two intervals was at the top. A second experiment indicated that subjects really do consider the intervals to be equal. Our findings argue for giving subjects a chance to reflect on such apparent inconsistencies in practical utility elicitation. (C) 2002 Elsevier Science (USA). All rights reserved.