Tactical Voting in Plurality Elections

TL;DR

This paper investigates tactical voting in plurality elections, introducing a model that explains vote polarization, small victory margins, and poll impacts across multiple countries and election types.

Contribution

It presents a novel model capturing tactical voting effects, explaining election anomalies and vote distributions in various electoral contexts.

Findings

Model explains vote polarization and small victory margins.

Reproduces vote distributions in Brazilian mayor elections.

Analyzes poll impacts in American, Canadian, and Brazilian elections.

Abstract

How often will elections end in landslides? What is the probability for a head-to-head race? Analyzing ballot results from several large countries rather anomalous and yet unexplained distributions have been observed. We identify tactical voting as the driving ingredient for the anomalies and introduce a model to study its effect on plurality elections, characterized by the relative strength of the feedback from polls and the pairwise interaction between individuals in the society. With this model it becomes possible to explain the polarization of votes between two candidates, understand the small margin of victories frequently observed for different elections, and analyze the polls' impact in American, Canadian, and Brazilian ballots. Moreover, the model reproduces, quantitatively, the distribution of votes obtained in the Brazilian mayor elections with two, three, and four candidates.