The influence of time and adaptation on health state valuations in patients with spinal cord injury.

Objectives: One of the explanations for the difference between health state utilities elicited from patients and the public--often provided but seldom studied--is adaptation. The influence of adaptation on utilities was investigated in patients with spinal cord injury.

Methods: Interviews were held at 3 time points (T1, after admission to the rehabilitation center; T2, during active rehabilitation; T3, at least half a year after discharge). At T1, 60 patients were interviewed; 10 patients withdrew at T2 and T3. At all time points, patients were asked to value their own health and a health state description of rheumatoid arthritis on a time trade-off and a visual analogue scale. The Barthel Index, a measure of independence from help in activities of daily living, and the adjustment ladder were filled out. Main analyses were performed using mixed linear models taking the time-dependent covariates (Barthel Index and adjustment ladder) into account.

Results: Time trade-off valuations for patients' own health changed over time, even after correction for gain in independence from help in activities of daily living, F(2, 59) = 8.86, P < 0.001. This change was related to overall adaptation. Both a main effect for adaptation, F(87, 1) = 10.05; P = 0.002, and an interaction effect between adaptation and time, F(41, 1)= 4.10, P = 0.024, were seen for time trade-off valuations. Valuations given for one's own health on the visual analogue scale did not significantly change over time, nor did the valuations for the hypothetical health state.

Conclusion: Patients' health state valuations change over time, over and above the change expected by the rehabilitation process, and this change is partly explained by adaptation. Experience with a chronic illness did not lead to change in valuations of hypothetical health states.