As with all full representation, cumulative voting (CV) requires representatives to be elected from multi-seat districts -- districts with more than one representative. Voters in each district have as many votes as there are seats to be filled, as would be true in a plurality election, but CV allows voters to express a strong preference for their favorite candidate or candidates. Unlike plurality, they are not restricted to giving just one vote to a candidate. If like-minded voters in a political minority concentrate their votes on one candidate in a three-seat election, for example, they can win representation despite their minority status. In a three-seat district elected by cumulative voting, a candidate can be sure of winning one seat with the support of about 25 percent of voters.
There are two varieties of cumulative voting.
- Free cumulative voting: In free CV, voters may allocate their votes in any manner they choose. For instance, in a district electing five seats to a legislature, voters would cast five votes and could split them up as they chose: all five votes for their favorite candidate, perhaps, or three votes for one candidate and two votes for another, or any other combination adding up to five votes. The five candidates winning the highest number of votes are elected.
- Equal and even cumulative voting: In equal and even CV, voters cast votes for as many candidates as they prefer, and their votes are allocated equally among those candidates. In a five-seat race, voting for just one candidate would give that candidate five votes. Voting for two candidates would give each one 2.5 votes, and voting for four candidates would give each candidate 1.25 votes. Equal and even CV (also called the Peoria method, as it is used to elect the at-large city council seats in Peoria, IL) makes it easier for candidates to run as a team.
CV tends to elect legislatures that more fairly reflect the make-up of the populations they represent than winner-take-all elections, as both majorities and minorities can be represented in rough proportion to their popular support. And because it allows for successful independent candidacies, CV is an attractive alternative in political situations where individual candidates are seen as more important than party politics, as is often the case in the United States.
CV, however, has its drawbacks. One is the problem of a like-minded constituency splitting its vote. For example, if a voting constituency or a political party has too many candidates, it can "split" its votes among its own competing candidates and not win a fair share of seats. Candidates also must compete aggressively against candidates in their party – such intra-party competition can undercut coherent parties. In order to prevent vote splitting and intra-party competition, a party or like-minded constituency often seeks to limit candidacies and organize individual voters to allocate their ballots among those candidates. As a result, some argue that CV can concentrate too much power in the hands of leaders of parties or non-partisan communities of interest.
CV has been used to settle many voting rights cases since initial settlements in the late 1980s in places such as Chilton County (Alabama), Alamogordo (New Mexico) and Peoria (Illinois). More than 50 jurisdictions in Texas have adopted cumulative voting in the 1990s, including Amarillo for elections to its school board. Cumulative voting also has been imposed by federal judges in three voting rights cases, as of June 2000, but has yet to be upheld by higher courts.
There is also a growing movement to restore CV for state legislative elections in Illinois, where it was used to elect the state’s house of representatives from 1870 to 1980, producing numerous advantages over the current single-seat districts used in Illinois. Backers include former Republican governor Jim Edgar and the Democratic head of the state senate Emil Jones. Some major corporations use CV to elect their board of directors.