Ideological distances predict vote shifts in french two round elections
The Geometry of Alliances: Vote Transfer Modelling in French Two-Round Elections
Computer Science and Game Theory
Summary
In two-round elections, votes from parties that don’t make it to the second round often shift to other candidates in ways that are hard to predict. The authors created a model that uses detailed measures of political beliefs to guess how these votes move between candidates. They tested the model on recent French elections and found it accurately explained most vote changes, especially when more than two groups made it to the second round. This shows that simple left-right political views aren’t enough to understand voter behavior, and more complex ideas about ideology matter a lot.
What this means in practice
- •For political campaign teams: Predict voter shifts between rounds in multi-party elections to tailor campaign strategies effectively under complex ideological conditions.
- •For electoral strategy analysts: Model vote transfers more accurately than simple left-right scales for better election forecasting and scenario planning in multi-round contests.
Authors
Emmanuel Omont
Abstract
Two-round legislative elections are decided not only by first-round vote shares, but by how voters whose preferred party did not advance redistribute their votes among the surviving candidates. We develop a principled model of this transfer process, grounded in multi-dimensional ideological embeddings derived from the Chapel Hill Expert Survey, and apply it to French legislative elections. Calibrated on the 2017 and 2022 elections, the model is evaluated on the unusually complex 2024 contest, in which three ideologically distinct blocs reached the second round simultaneously, achieving 90.34 percent constituency-level accuracy. We show that ideological proximity alone explains the large majority of vote transfers, that a simple left-right axis is insufficient to capture the relevant distances, and that the structural configuration of the 2024 electorate was far less favorable to the far right than pre-election forecasts suggested.