Information Aggregation with Runoff Voting

A majority of independent voters wants to choose the alternative that better matches the state of the world, but may disagree on its identity due to private information. When we have an arbitrary number of alternatives and also sophisticated partisan voters exist in the electorate, the election of the correct alternative is a real challenge. Building upon McLennan (1998) and Barelli et al. (2017) we show that runoff voting -one of the most intuitive electoral systems- achieves asymptotically full information equivalence. That is, when the society is large, it can lead to the election of the correct alternative under fairly general assumptions regarding the information structure and partisans' preferences.