National Polls, Local Preferences and Voters’ Behaviour : Evidence from the UK General Elections

A central challenge for social scientists consists in explaining why people vote and what are the consequences of their behaviour. Exploiting variation in national opinion polls across UK general elections, and in the degree of safeness of British constituencies over time, I provide evidence of a significant impact of pre-election polls on electoral outcomes and shed light on a novel mechanism. I find that opinion polls affect voters’ behaviour via their interaction with the recent electoral history of a constituency : first, turnout decreases when the polls predict non-competitive elections, and this effect is stronger in safe seats. Second, the composition of local vote shares and parties’ performance is also impacted by anticipated election closeness and the effects vary heterogeneously depending on whether polls predictions are aligned with the past electoral outcomes of a constituency. Finally, the causal impact on voters’ participation is confirmed with consistent individual-level evidence.