When Knowledge Counts Twice: The Role of Turnout in EU Referendums

Aggregate data on EU referendums indicate that turnout has a significant impact on the referendum outcome. Existing studies of referendums, however, tend to ignore non-voters and therefore miss an important part of citizens’ choice. This is problematic especially when individuals’ characteristics influence both the decision to turn out and the vote choice of those who decide to vote. Specifically, uncertainty about the consequences of a treaty – or, lack of subjective knowledge – affect both the vote choice and the decision to abstain. This means that there is an amplified effect of knowledge on voting behavior, first via turnout and second via vote choice. Extending previous work, this paper develops a formal theoretical model relating uncertainty to both turnout and vote choice, explicitly modelling the interdependence of these decisions. Using a statistical model that jointly estimates turnout, vote choice, and their interaction, on data related to a number of referendums on European integration, we show that in important cases, the estimated effect of uncertainty on referendum outcomes is significantly larger than when only the vote choice is considered.