Glossary of Key Electoral System Terms
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Glossary of Key Electoral System Terms Alternative vote One name for the use of the single transferable vote (q.v.) in a single seat district. In the USA, this method is often referred to as the instant runoff. Approval voting (AV) A method in which voters may cast up to as many votes as there are candidates, under the instruction to vote only for those can- didates/alternatives of which they approve, i.e., which they find acceptable. The candidates with the greatest number of approval votes are chosen. AV A common acronym for approval voting; it is also used as an acronym for alternative vote. Borda rule A method of ranked voting which assigns numerical scores to each candidate based on where they stand in each voter’s ranking (one point for each candidate they are ranked higher than) and then sums up those votes over all voters to obtain each candidate’s Borda score. Then, the candidate with the highest Borda score is chosen. Borda score See Borda rule. Closed list PR See List PR. Compensatory allocation In mixed member systems (q.v.) or in other systems that have multiple tiers of election, a method of allocating seats in higher tiers based on results in lower tiers that acts to increase the proportionality of seat outcomes to party vote shares. Condorcet extension method See Condorcet rule Condorcet rule The ranked voting method which chooses that candidate, if any, who can defeat all other candidates in paired (head-on-head) competition. Such a candidate is called a Condorcet winner,oramajority winner. Since there may be no such candidate, a variety of methods have been proposed as Condorcet extension methods, to choose. Condorcet winner See Condorcet rule Coombs rule Aformofrankedvoting(q.v.) similar to the alternative vote (q.v.), except that, instead of dropping the candidate with fewest first place votes, in the B. Dolez et al. (eds.), In Situ and Laboratory Experiments on Electoral Law Reform: 143 French Presidential Elections, Studies in Public Choice 25, DOI 10.1007/978-1-4419-7539-3, c Springer Science+Business Media, LLC 2011 144 Glossary of Key Electoral System Terms absence of any candidate who receives a majority of the votes cast, we drop the candidate with the most last place votes and then reallocate that candidate’s support. Cumulative voting (CV) An electoral rule in which voters have multiple votes to cast and are allowed to cumulate their votes on one or only a few candidates. There are many variants of cumulative voting, with perhaps the most common involving the requirement that all components of the allocation vector which sums to the num- ber of votes each voter is entitled to cast must be integers. CV The common acronym for Cumulative voting (q.v.). Deviation from proportionality A measure of the extent to which party vote shares and party seats shares are not identical. The two most common measures of deviation from proportionality are the Loosemore and Hanby (1971) index of dis- tortion, which is a function of the summed absolute differences between seat share and vote share, and the Gallagher index (Gallagher 1991), which is a function of the squared differences between seat share and vote share. d’Hondt rule (for list PR, q.v.) A proportionality rule in which we allocate seats to each party after an integer division of each party’s vote share, allocating seats to the parties with the M highest quotients of party shares, where M is the number of seats to be filled. Worldwide, this is the most common rule for specifying a proportional allocation. It is also a special case of what is called a divisor rule, i.e., one where the seat allocations go to the highest quotients obtained after division of party vote shares by a set of numbers. Other allocation rules include the Sainte-Lag¨ue rule in which the set of divisors are the odd numbers, rather than the integers (see Balinski and Young 1982 for more details). District magnitude (M) The number of seats that are allocated to a given constituency [see also single member district (SMD) and multimember district (MMD)]. Droop quota of votes [for list PR systems, q:v., or STV, q.v.)] This is equal to E/(M +1),whereE is the size of the actual electorate and M is the number of seats to be filled. Double ballot mixed system A mixed member electoral system in which voters cast one ballot to determine the outcome of the single member districts (q.v.) in which they are located and a different ballot to determine the party share for the proportional tier (q.v.) of the mixed system. Effective number of electoral parties (ENEP) This is a calculation of the Laakso- Taagepera (1979) index for party vote shares. To calculate this index, we take each party’s vote share, square it, sum the squares, and then take the inverse of the sum so obtained. When all r parties have equal vote shares, the L-T index will be r. The L-T index is the inverse of the Hirschman–Herfindahl index widely used in sociology and economics; it can also be linked to standard variance calculations (see Feld and Grofman 2007). Also see effective number of parliamentary parties. Glossary of Key Electoral System Terms 145 Effective number of parliamentary parties (ENPP) This is a calculation of the Laakso-Taagepera (1979) index for party seat shares. To calculate this index, we take each party’s vote share, square it, sum the squares, and then take the inverse of the sum so obtained. When all r parties have equal seat shares, the L-T index will be r. The L-T index is the inverse of the Hirschman–Herfindahl index widely used in sociology and economics; it can also be linked to standard variance calculations (see Feld and Grofman 2007). Also see effective number of electoral parties. Empty lists (also called short lists or sterilized lists) In the Italian mixed system (q.v.) adopted in 1993, a technical trick in creating party lists designed to avoid vic- tories in the plurality tier (q.v.) costing a party seats in the proportional component of the mixed system (for details, see di Virgilio 2002). ENEP The acronym for effective number of electoral parties (q.v.). ENPP The acronym for effective number of parliamentary parties (q.v.). Evaluation voting A variant of the method of majority judgment (q.v.) in which voters can evaluate candidates using one of three grades (see the Baujard and Igersheim chapter in this volume). Hare formula (for list PR, q.v.orSTV,q.v.) A proportionality rule in which we allocate seats to each party based on integer and greatest (largest remainder) frac- tional shares of total votes cast multiplied by the number of seats to be filled. See also Imperiali formula, d’Hondt rule, Droop quota, Hare quota. Hare quota of votes (for list PR systems, q.v., or STV, q.v.) This is equal to E/(M/, where E is the size of the actual electorate and M is the number of seats to be filled. Imperiali formula See Imperiali rule. Imperiali rule (for list PR, q.v.orSTV,q.v.) A proportionality rule used in Italy to list PR elections from 1956 to 1991, in which we allocate seats to each party based on integer and greatest (largest remainder) fractional shares of total votes cast divided by the number of seats to be filled plus two. See also Hare formula, d’Hondt rule, Droop quota. Instant runoff See Alternative vote. Laakso–Taagepera index See effective number of electoral parties (ENEP) and number of parliamentary parties (ENPP). Limited voting A system of voting in which voters in districts where there are M seats to be filled have only k votes to cast. One pole of limited voting occurs when k = 1; this is the single nontransferable vote (q.v.). List PR system In the list form of proportional representation; voters cast a (nor- mally single) ballot for a party list, and the number of candidates on each list who are elected is determined by the share of the votes received by each party In closed list PR, only parties are objects of choice and the parties determine rank of their own candidates so that a party which wins r seats will elect the top r candidates on 146 Glossary of Key Electoral System Terms its list of candidates; in open list PR, voters may also affect by their vote choices (even if not fully determine) which individual candidates from a given party will be elected by indicating their preferences among candidates. Flexible list PR is also sometimes distinguished from open list PR in that in flexible list PR, voters have the option of either casting a simple list vote or of voting for individual candidates whose preference votes may then place them ahead of the other candidates on the party list. List tier See Proportional tier. M A common acronym for District magnitude. Magnitude See District magnitude. Majoritarian voting rule A voting rule in which a majority of the voters, if they are able to coordinate their votes, could determine all the winners within any con- stituency. Majority judgment A new voting method proposed by Balinski and Laraki. It makes use of pre-specified grades assigned by voters to each candidate, and then looks for the candidate with the highest median grade, using a lexicographic rule to break ties (see their essay this volume for details). Majority runoff (two rounds) A particular form of runoff rule (q.v.) in which the top two candidates in the first round face off in head to head competition in the second round if no candidate received a majority of the votes in the initial round of voting.