Does the whole equal the sum of the parts? Patient-assigned utility scores for IBS-related health states and profiles

The quality-adjusted life year (QALY) assumes that the value of a health state is linearly related to the time spent in it, which implies that the value of a health state is independent of the states which precede or follow it. Irritable bowel syndrome (IBS) is a suitable condition to test this assumption since it is subject to considerable fluctuations over time. Forty-nine IBS patients were asked to rate their own health using generic measures of health and a condition specific classification. They were then asked to value five IBS states and four profiles using a self-completed version of the standard gamble technique. The implied value of each profile was estimated using the QALY assumption of linearity over time and compared with the direct profile valuations. The directly elicited profile values suggest that reductions in the duration of IBS symptoms has less of an impact on the value of quality of life than would be implied by the QALY assumption of linearity over time, though the differences were small. There are a number of competing explanations for this finding, including possible sequence effects, quantity effects or time preference, or it might be due to gestalt effects resulting in a neglect of time spent in symptomatic states of health.