Social Learning in Elections

Elections with sequential voting, such as presidential primaries, are widely thought to feature social learning and momentum effects, where the choices of early voters influence the behavior of later voters. Momentum may take time to build, and can depend on how candidates perform in each stage relative to expectations. This paper develops a rational theory of behavior in sequential elections that is consistent with these phenomena. We analyze an election with two candidates in which some voters are uncertain about which candidate is more desirable. Voters obtain private signals and vote in a sequence, observing the history of votes at each point. For a wide class of aggregation rules, we show that even strategic and forward-looking voters can herd on a candidate with positive probability, and such a “bandwagon” can occur with probability approaching one in large electorates.