On the Equivalence of Collectively and Individually Collected Responses

Abstract

The standard-gamble and time-tradeoff methods for valuing health states were com pared in a multifactorial design with 104 student volunteers. The main aim of the ex periment was to compare average individual responses with group responses for the same tradeoff tasks. Group responses were collected using an interactive voting sys tem. The standard EuroQol system was used to describe the health states to be val ued. Generalizability theory was used to analyze the results. The averages and median values of the individual responses differed from the interactively collected group values only for the more severe health states. The results showed almost identical results for the two methods, but the time tradeoff was found to be more consistent than the standard gamble. The authors conclude that 1) there is significant similarity between the results of individual and collective response modes, and 2) the standard-gamble and time-tradeoff methods produce almost equivalent values, despite their different conceptual backgrounds. In this study the aggregated individual responses and the collective response proved to be sufficiently similar to support the validity of using aggregated individual valuations as a measure of the valuation of the group. Key words: collective judgment; standard gamble; time tradeoff; methodology; voting sys tem ; EuroQol; generalizability theory. (Med Decis Making 1996;16:120-132)