An electoral or voting system is how votes are translated into seats. It determines how many votes and what kinds of votes are necessary to award seats to candidates and parties in an election. Different electoral systems produce different kinds of results, and give voters different kinds of choices.

The electoral system determines the “exchange rate” between votes and seats - that is, how votes are translated into seats.  How many and what kind of votes are needed to get a seat varies from system to system.  As a result, different electoral systems give politicians incentives to organize and campaign in different ways.  Some electoral systems may even create barriers for certain types of candidates.  Different electoral systems give voters different kinds of choices, which can then affect the decisions voters make.

A democratic electoral system can be said to be one where:

• elections are regular and fair
• votes are of equal value
• the will of the majority is achieved
• the interests of minorities are taken into consideration
• there is a high level of participation by the electorate
• there is the maximum possible franchise
• voting is accessible

• District Magnitude – this refers to the number of representatives elected from the district or riding. These could be single member ridings or multi-member ridings.
• Ballot Structure – this refers to the number of voting preferences given a voter on a ballot for them to mark. The range of choices includes a single choice for a party or candidate; a multiple preference between parties and candidates; and weighting preferences between candidates by rank-ordering them.
• Electoral Formula – this refers to the method by which votes are turned into seats, given the district magnitude and ballot structure being used. It could include thresholds stipulating the percentage of votes necessary to get elected.

There are several categorizations of electoral systems available. For simplicity we will recognize four categories here.

• Plurality Systems
• Majority Systems
• Proportional Reprsentation Systems
• Mixed Systems

We should however point out that even though the specific examples within each category may vary in a number of interesting ways all of them have common characteristics and appear to behave in similar ways with somewhat predictable consequences.

Also called “first-past-the-post” or “winner-take-all” systems, plurality systems simply award a seat to the individual candidate who receives the most votes in an election. The candidate need not get a majority (50%+) of the vote to win; so long as he has a larger number of votes than all other candidates, he is declared the winner.

The main features of plurality systems are as follows:

• Based on the principle that the contestant with the most support ought to be elected.
• Generally require simple and transparent voting and counting processes.
• Candidates are elected with a plurality (i.e. not a majority) of votes cast.
• Main models include: Single Member Plurality; Multi-Member Plurality (also called Block Vote).

First past the post voting (FPP)

This system of vote counting is the simplest - the voter only votes for one candidate and whoever gets the highest number of votes is elected. It is the easiest vote counting system to calculate results. The winning candidate is the one who gains more votes than any other candidate, but not necessarily an absolute majority (50% + 1).

FPP is used in the United Kingdom, Canada, India, the United States and many other countries.

Block vote (BV)

When the FPP system is used in multi-member electorates where electors have as many votes as there are seats to be filled it is known as the BV. Once a candidate is elected, all ballot papers are returned to the count to elect the next member. The highest-polling candidates fill the positions regardless of the percentage of the votes they actually receive.

The BV is used in Bermuda, Laos, Thailand, Kuwait, the Philippines and other countries.

Also called “second ballot” systems, majority electoral systems attempt to provide for a greater degree of representativeness by requiring that candidates achieve a majority of votes in order to win. “Majority” is normally defined as 50%-plus-one-vote. If no candidate gets a majority of votes, then a second round of voting is held (often a week or so after the initial ballot). In the second round of voting, only a select number of candidates from the first round are allowed to participate. In

The main features of majority systems are as follows:

• Based on the principle that an elected representative should be elected only if she or he has the support of more than half of the voters.
• May require preferential voting or more than one round of voting if there are more than two candidates, or a natural majority does not exist.
• Candidates are elected with a majority (i.e. more than 50%) of votes cast.
• Main models include: Alternative Vote; Two-Round Vote.

Preferential voting (PV)

PV is usually used in single-member districts and gives electors more options than FPP when marking their ballot paper. Electors must rank all candidates by placing the number ‘1’ for their preferred candidate and consecutive numbers from ‘2’ for their 2nd choice, ‘3’ for their 3rd choice and so on until all candidates are numbered. A candidate who has an absolute majority of votes (50% + 1) is immediately elected.

If no candidate has an absolute majority, the candidate with the lowest number of 1st preferences is eliminated, and their ballot papers are examined for 2nd preferences to be assigned to remaining candidates in the order as marked. The totals are then checked and this process is repeated until one candidate has an absolute majority.

PV is used in the Australian federal House of Representatives and in some state Legislative Assemblies. PV is also used in Nauru.

In OPV electors place the number ‘1’ for their preferred candidate and this is enough for a valid vote. They may continue numbering candidates in order of their preference to the extent they choose. All candidates do not have to be ranked.

NSW uses OPV for the election of representatives in the Legislative Assembly (Lower House) and in local government areas/wards for mayoral elections and when one or two vacancies are to be filled.

The TRS is conducted in the same way as an FPP election and if a candidate receives an absolute majority of votes, they are elected. If no candidate receives an absolute majority a second round of voting is conducted, often a week or two later and the winner of this round is declared elected. The 2nd round may be a contest between the two biggest vote winners (the Ukraine) or those who receive over a certain percentage of the votes of the registered electorate (France).

The TRS is used in countries such as France, Mali, Togo, Egypt, Iran, Belarus and Ukraine.

Proportional representation is the general name for a class of voting systems that attempt to make the percentage of offices awarded to candidates reflect as closely as possible the percentage of votes that they received in the election. It is the most widely used set of electoral systems in the world, and its variants can be found at some level of government in almost every country (including the United States, where some city councils are elected using forms of PR). 

The main features of Proportional Representation (PR) systems are as follows:

• Based on the assumption that parties are the real contestants and the principle that their seat shares should accurately reflect their vote shares
• Requires multi-member districts (the bigger the more proportional the final result can be)
• Counting and seat determination processes are generally complex and not immediately transparent
• Candidates are elected based on the total percentage of votes cast for their party.
• Main models include: List; Mixed Member Proportional; Single Transferable Vote; Single Non-Transferable Vote; Parallel.

Most PR systems use some form of List PR. List PR is used in multi-member electorates where votes are cast in order of preference for the parties which have registered a list of candidates. Parties receive seats in proportion to their overall share of the total vote and winning candidates are taken from the lists in order of their position.

MMP systems try to combine the elements of majority and PR systems. A proportion of the parliament is elected by majority methods, usually from single-member electorates, while the remainder come from PR Lists.

Under MMP systems, the List PR seats compensate for any disproportions produced by the district seat results. For example, if one party wins 10% of the national votes but no district seats, they would be awarded enough seats from the PR lists to bring their representation up to around 10% of the parliament.

MMP is used in countries such as Germany, New Zealand, Italy and Venezuela.

The STV system is used in multi-member districts with electors ranking candidates in order of preference on the ballot paper as in PV. Preference marking is usually optional where electors can mark as many candidates as they choose. After the total number of 1st preference votes is added up, the count begins by establishing the quota of votes needed for the election of a single candidate.

One of the most widely used methods is known as the Droop quota, named for the nineteenth-century thinker and mathematician H. R. Droop. The Droop quota is used to determine the minimal number of votes that an individual candidate must get in order to be awarded a seat. It is calculated using the formula:

                 [V/(S+1)] +1

where V is the total number of valid votes cast in the constituency, and S is the total number seats up for election in the constituency. Hence, if we have 1,000 votes cast for 3 seats, the Droop quota is [ 1,000 / (3 + 1) ] + 1 = 251. That means that any candidate who is able to get at least 251 votes will be assured of winning a seat. Once the Droop quota has been calculated and all the votes collected, we still have to allocate the seats. 

All Australian PR systems use the STV, although the South Australian, Victorian, Western Australian and NSW Upper Houses and the federal Senate may be thought of as semi-list systems as the ballot paper also provides for group voting above the line or in the case of Western Australia left and right of the line.

STV is used for national parliamentary elections in Ireland, Malta and Estonia.

In SNTV systems, each elector has one vote but there are several seats in the district to be filled. The candidates with the highest number of votes fill these positions. For example, In a 4-member district a candidate needs just over 20% of the vote to be elected.

The main difference between SNTV and majority systems is that the SNTV makes it easier for minority parties to be represented. The larger the number of seats in the constituency, the more proportional the system becomes.

The SNTV system is used for parliamentary elections in countries such as Jordan, Taiwan and Vanuatu.

Parallel systems use both PR lists and majority (“winner takes all”) methods but, unlike MMP systems, the PR lists do not compensate for any disproportions within the majority districts.

Parallel systems are used in around 20 countries including Croatia, Japan and Russia.

The main features of mixed systems are as follows:

• Involve combinations of the other four basic families within a single system
  
• Generally designed to introduce an element of proportionality
  
• May mix different types of electoral families across the entire country, or mix different types in different parts of the country
  
• Can produce legislators with different mandates, different constituencies, different roles