The impact of voter turnout on referendum outcomes: evidence from Ireland

We estimate the causal effect of voter turnout on referendum outcomes in Ireland using a newly created dataset that links 25 years of constituency-level referendum results to a variety of demographic and economic characteristics, as well as daily rainfall amounts. Our instrumental variables methodology uses rainfall as an instrument for voter turnout to overcome issues of endogeneity. By exploiting Ireland’s extensive experience with referendums, we are the first to explore the heterogeneous effects of turnout by referendum type (social issues versus regime-related issues). We find that a one-percentage-point increase in turnout is associated with a 1.6-percentage-point increase in support for progressively liberal social policies, which include issues such as same-sex marriage and abortion. For regime-related issues, such as EU economic treaties, we find no statistically significant effect of voter turnout on referendum outcomes. Our finding that turnout benefits socially progressive policies is consistent with a related strand of literature for general elections that indicates higher turnout benefits left-wing political parties.