Policy Motivation and Party Differences in a Dynamic Spatial Model of Party Competition

We present a model of party competition that produces more realistic patterns of results than those often emphasized in the literature. Reversing Downs (1957), we assume that parties win elections in order to formulate policies, rather than formulate policies in order to win elections. Voters are modeled first as having perfect information about candidate positions, and then under conditions of uncertainty. In simulation experiments we show that policy motivation and voter uncertainty can bring about persistent and predictable party differences in sequential majority rule elections. As the degree of voter certainty decreases, parties diverge towards their optima, whereas increases in voter certainty draw parties towards cycles in which party positions vary, but predictable issue stances are maintained on the average.