Electoral Turnout with Divided Opposition

We model costly, strategic voting in an electorate divided between a single pro-incumbent and multiple pro-opposition groups, and study the effect of the homogeneity of preferences within the opposition electorate on voter turnout. If each opposition group is represented by a separate candidate, there is a free-rider effect: the opposition turnout is lower if different opposition candidates are more substitutable. If there is a single pro-opposition candidate, the effect is the opposite under the proportional representation, and under a winner-tale-all system it depends on the size of the opposition, weighted by the intensity of preferences toward the opposition candidate. The weighted size of the opposition electorate also matters for how preference homogeneity affects incumbent vote share under proportional representation