A trial for comparing methods for eliciting treatment preferences from menwith advanced prostate cancer - Results from the initial visit

OBJECTIVE. The objective of this study was to evaluate the convergent valid ity of 3 types of utility measures: standard gamble, time tradeoff, and rat ing scale. RESEARCH DESIGN. A prospective cohort of 120 men with advanced prostate can cer were first asked to rank order 8 health states, and then utility values were obtained from each participant for each of the 8 health states throug h 2 of the 3 techniques evaluated (standard gamble, time tradeoff and ratin g scale). Participants were randomly assigned to 1 of 3 possible pairs of t echniques. The validity of the 3 methods, as measured by the convergence an d raw score differences of the techniques, was assessed with ANOVA. The abi lity of the techniques to differentiate health states was determined. The i nconsistencies between rankings and utility values were also measured. Prop ortions of illogical utility responses were assessed as the percent of time s when states with more symptoms were given higher or equal utility values than states with fewer symptoms. RESULTS. There were significant differences in raw scores between technique s, but the values were correlated across health states. Utility values were often inconsistent with the rank order of health states. In addition, util ity assessment did not differentiate the health states as well as the rank order. Furthermore, utility values were often illogical in that states with more symptoms received equal or higher utility values than states with few er symptoms. CONCLUSIONS. Use of the utility techniques in cost-effectiveness analysis a nd decision making has been widely recommended. The results of this study r aise serious questions as to the validity and usefulness of the measures.