PREFERENCE AGGREGATION IN THE HEALTH UTILITIES INDEX MARK 2 AND 3
Method: The HUI2 and HUI3 assign a utility to a health state by aggregating individuals’ preferences into a community scoring function. This is done by taking the average of individuals’ utilities for a health state as “the” utility of that health state. Social choice theory (Arrow, 1951; Sen, 1970) describes the contexts in which various preference aggregation methods are normatively justified. We describe the aggregation procedures used in the HUI2 and HUI3 in the framework of social choice theory and apply results from social choice theory to the HUI context.
Result: Examining the HUI2 and HUI3 through the lens of social choice theory, we investigate the assumptions that must be satisfied to justify relying on the average. For example, excluding individuals based on “illogical” responses (e.g., preferring a state with lower functional capacity to a state with higher functional capacity) creates normative problems for using the average as the mechanism of preference aggregation. Similarly, excluding individuals who report no differences between health states has strong implications for the normative foundations of the aggregation procedure. Social choice theory also provides alternatives to the average. For example, a minimum or maximum aggregation method may identify subgroups of interest while an aggregation method that is a function of the standard deviation may address concerns with equity. Thus, aggregation methods embody different values and we describe policy scenarios in which an alternative aggregation method may be preferred.
Conclusion: The current use of the average as the method of preference aggregation is justified under explicit assumptions. This method ignores aspects of decision-making that may be relevant to societal decisions such as the equity of outcomes. There exist theoretically strong alternatives that capture distributional properties ignored by the average. Alternative procedures could be used in sensitivity analysis, ensuring the average is not ignoring some aspect of the heterogeneity of preferences that is relevant to the decision at hand.