Single-member district
Single Member systems, also called Single Winner systems, elect a single winner. These can be combined into many single member systems run independently in districts to form a Regional System.
They can be classified by ballot type:
- Plurality Voting: A valid vote can choose only one candidate
- Approval Voting: A valid vote can only give a yes or nothing to a given candidate.
- Ordinal Voting: A valid vote can rank candidates 1,2,3... (Tied rankings are permitted in some methods but not others)
- Cardinal Voting: voting A valid vote allows independent numerical values to be associated with each candidate. (The set of valid values is limited.)
Classification
They can be sub-classified by different ways to aggregate the ballots.
Plurality Voting
There is only one way to combine plurality votes.
Approval Voting and Cardinal Voting
Since Approval is the degenerate case of Cardinal Ballots they have the same A sum would give the Utilitarian_winner while a median would give the majoritarian winner.
Ordinal Voting
Borda count and Instant-runoff voting are common aggregation methods
Popular Single Member systems
- Plurality Voting: A valid vote can choose only one candidate
- Ordinal Voting: A valid vote can rank candidates 1,2,3... (Tied rankings are permitted in some methods but not others)
- Tied rankings not permitted
- Instant-runoff voting (IRV, also known as alternative vote or "preference voting")
- Supplementary vote: simplified IRV process (two rankings, two rounds)
- Borda count: single round count, more points for higher-ranked
- Coombs' method: disapproval runoff
- Tied rankings permitted
- Condorcet method, actually several families of systems that satisfy Condorcet's criterion:
- Ranked Pairs (RP) and variants such as Maximize Affirmed Majorities and Maximum Majority Voting
- Schulze, which is also known as "Beatpath Method" or "Cloneproof Schwartz Sequential Dropping"
- Copeland's method
- Condorcet-compliant methods
- VOTE-123: another name for Condorcet methods, stands for Virtual One-on-one Tournament Elections using 1st, 2nd, & 3rd choices
- Majority voting or Maximum Majority voting: another term often used for Condorcet methods
- Bucklin voting: approval with virtual runoff; each voters' ballot is counted for more candidates each round until some candidate reaches a majority
- Tied rankings not permitted
- Cardinal Voting: voting A valid vote allows independent numerical values to be associated with each candidate. (The set of valid values is limited.)
They can also be classified on how many times votes can be counted. Methods like Plurality, Borda, and Approval with single counting rounds are simpler since voters can be sure to know how their votes will be applied.
Single Winner Variations
- Automatic Equal Ranking Line Option (AERLO)
- A voter may mark a line in his/her ranking, meaning that if no one above that line wins, then that voter wants to promote to 1st place all of his/her above-line candidates and have a recount. (In pairwise-count methods the promotion only takes place if, additionally, there's a circular tie containing above-line and below-line candidates).
- Automatic Truncation Line Option (ATLO)
- A voter may mark a line in his/her ranking, meaning that if no one above the line wins, then that voter wants to drop from his/her ranking all of his/her below-line candidates and have a recount. (In pairwise-count methods the dropping only takes place if, additionally, there's a circular tie containing above-line and below-line candidates).