The bandwagon effect in two-round elections: evidence from inter-party races in the State of Louisiana

Abstract

Two-round elections are widely adopted in electoral systems worldwide due to their perceived strategy-proof nature. However, evidence suggests the occurrence of a bandwagon effect within these systems, where voters deviate from their true preferences in favor of the candidate previously expected to win, creating a self-replicating cycle where an initial first-round lead predicts a subsequent win. This study exploits Louisiana’s unique electoral system to examine whether voters exhibit such behavior in two-round elections with a strict two-party system. By analyzing an unbalanced panel of all two-round elections with inter-party competition held between 1975 and 2022, this paper investigates whether a candidate’s lead in the first round increases during the second round of voting. The findings reveal evidence supporting the occurrence of the bandwagon effect, with leading candidates experiencing a roughly 10-12% increase in their lead, even after controlling for state-wide swings, electorate composition, and coalition-building during the runoff stage. Interestingly, this effect is observed when the data is presented by individual candidates but not when it is grouped by party affiliation of the candidates. Further analysis utilizing an ecological inference framework demonstrates that the bandwagon effect is primarily driven by diverging patterns in turnout for voter groups of the top two candidates. This gap favors the candidate that leads into the runoff. In the second round of voting, the voter groups that support the leading candidate turn out at significantly higher rates compared to those supporting the candidate who placed second during the first round, which widens the gap in the runoff election. Results also show that voters engage in this behavior only in elections that are placed at the top of the ballot.