The Impact of Turnout in Optional Simultaneous Presidential Primaries on the Vote Share for the Coalition Candidate in the General Election: Evidence from Chile’s Two-Round System

Objective/context: We assess the effect of turnout in multiparty-coalition presidential primaries on the electoral support for the primary winner in two-round presidential elections. Does holding presidential primaries have a positive impact on the vote share received by the primary winner and/or political party in the corresponding presidential election? Methodology: We use municipal-level data in the three election cycles (2013-2021) since adopting optional presidential primaries in Chile to estimate ordinary least squares (OLS) models and assess the effect of turnout in the primaries on vote share in the general election. Conclusions: We identify a positive association between turnout in the primaries and vote share for the coalition candidate in the presidential election, with a higher impact on the runoff than in the first round. Originality: As primaries mobilize more ideological voters, the effect of primary turnout is stronger in the runoff when voters are more likely to align along clearly defined ideological lines than in the first round when primary voters normally have more than one option that matches their ideological preferences.