Electoral Systems 101

There are an infinite number of electoral systems—the rules that govern the conduct of elections and determine the winners. Every town, city, state, nation, and groups of nations across the world uses a different electoral system. Each choice about electoral systems reflects particular goals, values, and interests. Each choice also has consequences for the character of politics and democracy within a polity.

As an introduction to electoral systems, this primer describes key concepts necessary for analyzing an electoral system or reform to electoral system, grouped into three areas:

1.       The geography of elections

2.       The number of winners per contest

3.       The logic of choosing winners

Electoral systems can use any combination of single-winner and multi-winner contests. Executive offices such as mayor or lieutenant governor tend to lend themselves to single-winner contests, since there is typically only one office per polity. When there are multiple offices to elect, such as in the case of legislative bodies or regional courts, the chief considerations when deciding district magnitude are the desire for multi-party or minority representation and the extent to which politically salient constituencies are geographically concentrated.

Generally, as district magnitude increases, the greater the number of political parties in the legislature and the larger the proportion of seats that third party and independent candidates win. Multi-winner systems are associated with greater proportions of women in legislatures.

As district magnitude decreases, the population and size of districts (relative to their size with a higher district magnitude) decreases. For this reason, it is easier to draw (or gerrymander) single-winner districts that encompass politically salient constituencies, like a community of color, than it is in multi-winner districts. For this reason, single-winner districts have been favored in the United States as a way to ensure some representation to African American communities in cities with high levels of geographic segregation. 

The Logic of Choosing Winners

Electoral systems reflect different ideas about what it means to “win.” The most common idea is that whichever candidate(s) gets the most votes in a particular contest wins that contest, without any regard for the composition of larger elective body or set of representatives (“plurality”). Alternatively, a system may demand that the winner wins a majority of votes, either in a particular contest or across the polity, or both. Finally, an electoral system may seek to achieve representation that is proportional to the vote across the polity.

• Plurality: Winner(s) must get the most votes to win, irrespective of whether (in a single-winner contest) they received half of more of the votes.

• Majority: Winner(s) must win a majority (more than half) of the votes to win. Single-winner majoritarian systems typically employ a device to whittle the field to two (like ranked-choice voting or runoffs) to manufacture a majority when one does not exist naturally.

• Proportional: Winners are determined in multi-winner contests proportionally to the aggregate number of votes for each party or candidate. For example, if a party wins 25% of the vote, they should win close to 25% of the seats.

In plurality and majority systems, a large number (even a majority) of voters can cast votes that do not contribute to election a candidate. Proportional systems use information from more voters votes to elect a set of candidates in proportion to the overall vote.