Information, individual errors, and collective performance: Empirical evidence on the Condorcet Jury Theorem

Abstract

The Condorcet Jury Theorem implies that the collective performance of a group, in arriving at a “correct” judgment on the basis of majority or plurality rule, will be superior to the average performance of individual members of the group, if certain apparently plausible conditions hold. Variants of the Jury Theorem are reviewed, particularly including the politically relevant variant that allows for conflicting interests within the group. We then examine two kinds of empirical data. First, we compare individual and collective performance in a large number of multiple-choice tests, and we find that collective performance invariably and substantially exceeds average individual performance. Second, we analyze American National Election Study data to create dichotomous-choice tests concerning positions of candidates on a variety of political issues; Condorcet-like effects are again evident. Finally, continuing to use NES data, we construct, on each political issue, a simulated referendum (direct voting on the issue) and election (indirect voting on the issue by voting for candidates on the basis of their perceived positions on the issue), and we compare the two results. Despite high rates of individual error, electoral error is quite small, and collective performance is fairly high, providing evidence of Condorcet-like effects in situations of conflicting preferences.