In my previous article I discussed the types of plurality-majority voting we use in this country and introduced the principle of proportional representation: majority rule with minority representation, in proportion to voting strength in the electorate. In this article I will describe the three main systems of proportional representation: List PR, Mixed Member Proportional (MMP), and Choice Voting (CV). Both List PR and MMP require partisan elections, whereas CV is amenable to both partisan and non-partisan elections.
In List PR, political parties prepare ordered lists of candidates and publish them before the election. Voters vote for the party of their choice, and seats are allocated to the parties based on the percentage of vote they receive. Parties then fill the seats with the candidates on their lists, in order. (Some List PR systems allow the voters to affect the order in which candidates are chosen to fill seats.) List PR is used by most of Western Europe, most of South America, and post-apartheid South Africa, among other countries. It is also used by the Democratic Party in selecting delegates to its national convention (since each presidential candidate prepares a list of delegates that supports them, and is allocated a number of delegates in proportion to the vote they receive in each primary or caucus).
Mixed Member Proportional combines List PR with single-member districts. Each voter gets two ballots; one lists candidates running from their district, and one lists all the parties involved. A certain number of seats (usually about half) are reserved for the party lists. After the winners of the single-member districts are determined, the party list seats are allocated in a compensatory fashion so that the total percentage of seats each party receives corresponds to the percentage of the party list vote received. MMP is used by Germany, Hungary, Mexico, Venezuela, and New Zealand, among other countries.
In Choice Voting (CV), a voter is presented with a list of candidates. The voter writes a "1" next to their first choice, a "2" next to their second choice (who they would want if their first choice were eliminated), etc., for as many choices as they desire. Note that the voter can number more candidates than there are seats to be filled; in fact, it is in the voter's interest to do so.
A threshold of election is established by dividing the number of ballots cast by one more than the number of seats to be filled, and then adding one. The ballots are then sorted by first preference. If no candidate is over the threshold of election, the candidate with the fewest votes is eliminated and those ballots transferred to their respective second choices. This process is repeated until one (or more) candidates are pushed over the threshold.
Whenever a candidate has more votes than the threshold, that candidate is declared elected, and the "excess votes" (the total received less the threshold) are distributed to their next choices. (For example, let's assume a 9-seat election and a voting population of 100,000, so the threshold is 10001 votes. If a candidate were to receive 40004 first-choice votes, the excess would be 30003.) The process of first transferring excess votes, and then transferring votes from eliminated candidates, repeats until all the seats are filled.
How the excess votes are selected for transferring is one of those details that differentiates CV systems. Some select ballots at random, some assign a fractional weight to the "last transferred" ballots, some assign a fractional weight to all the ballots. (In the example, since only 1/4 of each of these ballots was needed to elect the candidate, each of these ballots has 3/4 of a vote that is, in a sense, unused. So each of these ballots would be assigned a value of 3/4 and transferred to their respective second choices.) Because CV frequently requires that a candidate receive second-choice (or later) ballots in order to be elected, the incentive for negative campaigning is reduced.
CV is used in Ireland and Malta, and to elect the Australian Senate. It is also used to elect the community school boards in New York City, the school board and city council in Cambridge, Massachusetts, and to select the nominees for the Academy Awards.
In my next article I will discuss a relative of CV that can be used when a single winner is to be elected, as in an election for Mayor or President.
Steve Chessin is an Advisory Board member of Fairvote, and serves on the Board of Directors of Californians for Electoral Reform.