Efficacy, power and equity under approval voting

Approval voting allows each voter to vote for as many candidates as he wishes in a multicandidate election. Previous studies show that approval voting compares favorably with other practicable election systems. The present study examines the extent to which votes for different numbers of candidates can affect the outcome. It also considers generic powers of voters and the extent to which approval voting treats voters equitably. If there are three candidates, votes for one or two candidates are equally efficacious in large electorates. For four or more candidates, votes for about half the candidates are most efficacious. Although inequities among voters can arise under approval voting, the common plurality voting system is considerably less equitable than approval voting.