Aggregation of Value Judgments Differs from Aggregation of Preferences

Abstract

This paper focuses on the contrast between aggregation of individual preference rankings to a collective preference ranking and aggregation of individual value judgments to a collective value judgment. The targeted case is one in which the two aggregation scenarios exhibit a far-reaching structural similarity: more precisely, the case in which the individual judgments that are to be aggregated are value rankings. This means that, formally, the individual judgments are isomorphic to individual preference rankings over a given set of alternatives. The paper suggests that, despite of their formal similarity as rankings, the difference in the nature of individual inputs in two aggregation scenarios has important implications: the kind of procedure that looks fine for aggregation of judgments turns out to be inappropriate for aggregation of preferences. The relevant procedure consists in similarity maximization, or -more precisely -in minimization of average distance from individual inputs. It is shown that, whatever measure is chosen, distance-based procedures violate the (strong) Pareto condition. This seems alright as value judgment aggregation goes, but would be unacceptable for preference aggregation.When applied to judgment aggregation, distance-based procedures might also be approached from the epistemic perspective: questions might be posed concerning their advantages as truth-trackers. From that perspective, what matters is not only the probability of the outcome being true, but also its expected verisimilitude: its expected distance from truth.Key words: preference aggregation, judgment aggregation, preference, value judgment, distance-based methods, Pareto, Condorcet's jury theorem, distance measures, verisimilitude, truth-tracking, Kemeny.The point of departure in my story is the contrast between two models of democratic voting: popular democracy, as exemplified by popular elections and referenda, and what might be called committee democracy, i.e., voting in smaller bodies of experts or specially appointed laymen. What is the difference between these two models, viewed as ideal types? On one

Aggregating Moral Preferences

“…The absence of a foundational commitment to strong Pareto is one important difference between the metaethical variant of preference aggregation and these other variants (cf. Rabinowicz 2015).…”