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PURPOSE: In prospect theory (PT) value is defined in terms of gains and losses from a reference point, with a value function which is convex and relatively steep for losses and concave and not so steep for gains. Our objective was to examine PT postulates in the valuation of a hypothetical osteoarthritis (OA) state, using current health status as the reference point for valuation.
METHODS: We surveyed 391 subjects (198 patients with OA and 193 community members). Participants were interviewed and asked to rate their own health, as well as vignettes describing patients with OA using visual analog scale (VAS), standard gamble (SG), time trade-off (TTO) and willingness to pay (WTP). For this analysis we used a scenario based on EQ-5D domains, describing an individual with mild to moderate OA (York tariff=0.69). Subject valuations of this state were examined in relation to the difference score between the state and their own health (gains/losses) as determined by EQ-5D York tariffs.
RESULTS: In the public, 27.2% had worse health status than the vignette, 9.9% had similar health, and 68% had better health. For the patient group, the percentages were 50.5%, 16.7%, and 32.8%, respectively. The difference score between the scenario and current health was related to the valuations of the scenario as follows (Spearman correlation: VAS r=-0.06 (p=0.22); SG r= 0.35 (p<0.001); TTO r= 0.15 (p=0.004); and WTP r=-0.10 (p=0.10). As postulated in PT, individuals perceiving the hypothetical state as a gain in health (positive difference) were less likely to trade or gamble, than individuals who perceived the hypothetical state to be a loss (negative difference). With SG, the slope was steeper for losses than for gains, with no major differences seen with the other techniques. Overall however, the predictive value of current health as a reference point was low.
CONCLUSION: Our findings suggest that subjects’ valuation of arthritis states follow PT principles when using SG, and to a lesser degree TTO. Yet, the explanatory power of current health as a reference point is weak, suggesting that other unrelated factors may play a more important role in patients’ preferences as elicited by these techniques.
See more of Oral Concurrent Session A - Judgment and Decision Making
See more of The 26th Annual Meeting of the Society for Medical Decision Making (October 17-20, 2004)