Efficacy in small electorates under plurality and approval voting

Assuming independent voting and random tie-breaking, we describe a procedure for computing the efficacy of a voting strategy under approval voting (AV) and plurality voting (PV) in single winner elections. When the number of candidates exceeds three, the voter's efficacy — his or her ability to affect the outcome of an election — is greater under AV than PV. The relative advantage of AV over PV increases as the number of voters or number of candidates increases.This study has been supported by grant 84-00329 of the U.S.A.-Israel Binational Science Foundation (BSF), Jerusalem, Israel, in collaboration with Steven Brams and Zeev Maoz.