Assessing the psychological and mechanical impact of electoral rules: A quasi-experiment

The paper assesses the influence of electoral rules on vote choice and election outcomes using a quasi-experiment conducted during a recent Canadian provincial election. Respondents were invited to vote under three voting systems (first past the post, alternative voting and proportional representation) and to answer a short questionnaire. We examine how the distribution of votes and seats is affected, and we ascertain how much of the total difference is due to psychological and mechanical effects. We find that a PR system would have increased legislative fractionalization by the equivalent of one effective party and that the mechanical effect is much more important than the psychological effect. As for AV, its mechanical and psychological effects act in opposite directions.