Probabilistic Voting Model

The probabilistic voting model is a formal theory of electoral competition in which each voter's choice between two parties is treated as stochastic rather than deterministic, governed by a smooth probability that depends on the policy utilities the parties offer plus idiosyncratic and partisan preference shocks. Developed by Assar Lindbeck and Jörgen Weibull in 1987 and given its general treatment by Peter Coughlin in 1992, the model replaces the knife-edge switching of the median voter framework with continuous vote-share functions. Two office-seeking parties maximize expected vote share, and the resulting equilibrium maximizes a density-weighted social welfare function in which the most responsive — the swing — voters carry the greatest weight. Crucially, the model delivers a determinate, interior equilibrium even in multidimensional policy spaces where a Condorcet winner generically fails to exist.