The Effectiveness of the Plurality Rule

Plurality (first-past-the-post), majority and proportional electoral formulae all translate vote shares into seat shares in different ways. The consequences of these differences are the subject of a large literature, and the virtues and vices attributed to the plurality rule are particularly numerous. That is not surprising given the discrepancies between seat and vote shares it generates. What is surprising is that the literature has not examined the plurality rule's effectiveness, that is the extent to which it achieves its intended goals. We take effectiveness to be a necessary, though not sufficient, condition for an electoral rule's acceptability. At the very least, a given rule ought to produce the consequences it is designed to create. This short Note is intended to assess the extent to which the plurality system passes this minimum test.