Nash equilibrium in multiparty competition with ‘stochastic’ voters

Theoretical spatial models of electoral voting tend to predict either convergence to an electoral mean (when voting is probabilistic) or chaos (when voting is deterministic). Here, we construct an empirical model of voting for the Israeli Knesset in 1992 (based on a large electoral sample and on analysis of party declarations). The probabilistic voting model so estimated fits the known election results. We then use the same model to simulate the effect of expected vote maximization by the parties. Contrary to the usual results, there is no unique convergent Nash equilibrium under this objective function. We do infer, however, that the two large parties are ‘Downsian’, in the sense that they maximize expected vote (up to the margin of error of the model). We suggest that the empirical results are compatible with a hybrid model of utility maximization, where each party computes the effects of its policy declaration both in terms of electoral response and of post-election coalition negotiations.