Electoral Systems 101
Choosing our elected representatives is complex.
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
The Geography of Elections
Elections can happen in a set of districts (with separate contests) that together form a polity or “at-large,” with the same contest across the whole polity.
District: A geographical subregions into which a city, county, state, or country is divided for election purposes.
At-large: A single contest that takes place across the whole polity, such as a whole city, county, state, or nation.
Electoral systems can elect representatives by district, at-large, or a combination of the two. Executive offices such as mayor or lieutenant governor are usually elected at-large, 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, choosing between districts and at-large election largely comes down to whether the polity wants to represent geographically distinct constituencies, such as those defined by race and ethnicity, economic interests, or local identity.
The Number of Winners Per Contest
A second part of the electoral system to consider is the number of winners elected per contest, technically known as “district magnitude.” Each district or at-large contest can elect one (in “single-winner” contests) or multiple officers (in “multi-winner” contests).
District Magnitude: The number of candidates elected in each contest.
Single Winner: A district or at-large contest in which only one office is elected. Also known as a “single member” or “single seat .”
Multi Winner: A district or at-large contest in which two or more offices are elected from the same set of candidates.
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.
In legislative elections, plurality and majority systems are ill-equipped to produce outcomes that reflect the total vote across the polity. The winner(s) of each contest are identified in isolation, without consideration of the overall make-up of the legislative body overall. This means a political party will often win a majority of seats in a body without winning a majority or even the most votes across the polity.
Unlike plurality and majority systems, proportional systems can only operate in multi-winner contexts. Proportional systems get more proportional the higher the district magnitude.
Proportional systems are designed to elect candidates and parties that do not have the most support, in addition to those that do, embracing the idea that it is not only the supporters of the most popular candidates who deserve representation.