Purpose: The standard gamble (SG) and time trade-off (TTO) are commonly used methods for obtaining health utilities, and many studies obtain utilities using both methods. However, because one method (SG) measures risk attitude and the other (TTO) does not, it is possible that order of assessment will alter the relative utility values obtained by each method. We sought to determine if the order in which SG and TTO utilities were obtained for the same outcomes affects the relative values of the utilities obtained by each technique.
Method: Utility values for 29 different health states were gathered from 4016 interviews. Utilities were obtained from each respondent with both SG and TTO. However, the order in which the methods were used was randomized by respondent. We calculated the difference between the utilities obtained by SG and those obtained by TTO for each assessment for all 29 health states. The mean difference between SG and TTO utilities in the SG-first group was compared to the mean difference in the TTO-first group using an independent samples t-test.
Result: For 20 of the 29 utilities the absolute difference between utilities assessed by SG and TTO was greater when the SG method was used first. The result of the t test was significant for 18 of the 29 different utilities. Moreover, when SG was used first the mean difference, SG –TTO, resulted in a negative value in 26 of the 29 assessment, suggesting risk-seeking behavior. Whereas, in 25 of the 29 analyses when TTO was used first the result was positive, suggesting risk aversion.
Conclusion: The order in which the SG versus TTO method is used strongly influences the relative values of the utilities obtained, suggesting a “halo” effect of the first assessment. When the SG is assessed first respondents exhibit more risk-seeking behavior.
Candidate for the Lee B. Lusted Student Prize Competition