Single Member Plurality Systems

Used to elect the U.S. House Representatives, as well as many state and local legislatures, The single member plurality election is the most common and best-known electoral system currently in use in America. Under single member plurality systems, an area is divided into a number of geographically defined voting districts, each represented by a single elected official. Voters cast a single vote for their district’s representative, with the highest total vote-getter winning election, even if he or she has received less than half of the vote.

In addition to the problems endemic to all winner-take-all systems, single member plurality results create some specific difficulties of their own. First, where the boundaries of districts are drawn can have a huge effect on who is likely to win election. As a result, gerrymandering to protect incumbents or weaken political enemies is common practice under single member plurality systems. Second, single member plurality elections are prone to the spoiler dynamic. Where more than two viable candidates run and split the vote within a district, the “winner” of an election can often be the candidate whom the majority of voters liked least. Generally, parties will limit the number of candidates running to avoid this scenario, leaving voters with minimal choice. These dynamics mean that voters have no effective choice, and are left to ratify the candidate of the majority party in their district.

Single member majority systems are identical to single-member plurality systems, except that they use two round runoffs or instant runoff voting to ensure that the winner of an election has the support of the majority of voters. While this eliminates the spoiler problem, it does nothing to stop the negative effects of gerrymandering or the limitations inherent in making geography the primary districting criteria. In some cases these systems can also make it harder for communities of color to win election.