Preferential choice

The title of this article is ambiguous. Further meanings are listed under preferred option (definition of terms ) .

The preferred choice is used in German in three meanings:

• In tourism , this means special requests that can be made when booking accommodation. Examples would be: extras in the accommodation, suitable for pets, in a permanent non-smoking area etc.
• In social choice theory , it is understood to be an electoral system . The individual decision alternatives are ranked by each voter in the order of their individual preference. From these different rankings, the group preference is then determined using special aggregation procedures - with individual procedures only the “winner”, with others a ranking of all alternatives.
• In everyday political use, preferential voting is used as a synonym for a special election process from social election theory, instant runoff voting , which is used in Australia and Ireland, for example.

The preferential choice in terms of social choice theory

Examples of aggregation methods for preferential voting are: Borda election , Condorcet method , Coombs election , Instant Runoff Voting (IRV), Ranked Pairs , Schulze method , Bucklin election . With the same individual ranking of the alternatives by the group members, depending on the aggregation method used, entirely different group preferences can arise.

Choice example

Consider a group of n = 21 people who choose a candidate from m = 3 candidates {A, B, C}. The members of the group have the following preferences.

6  0  5  2  5  3
----------------
a  a  b  b  c  c
b  c  a  c  a  b
c  b  c  a  b  a

Explanation: 6 people have the preference: a before b, a before c and b before c. (The lower case of the letters indicates individual preferences.)

• In the paired voting method ( Condorcet method ), candidate A wins against every other candidate. Candidate C loses to everyone else. Election result : A before B before C.
• The following election result arises from the Borda election. Candidate B gets 44 points, candidate A 43 and candidate C 39 points. Election result : B before A before C.
• With instant runoff voting , A is eliminated first (with 6 votes, the fewest first preferences) and his votes are transferred to the second preference, so that afterwards B wins with 13 votes before C with 8 votes. Election result : B before C before A.
• In the Coombs election , only C is eliminated (since he was placed last by 11 people) and his votes are transferred to the second preferences. Therefore, A wins with 11 votes against B with 10 votes. Election result : A before B before C.
• Note: With the simple majority method ( majority vote ), another candidate wins, namely candidate C with 8 votes. Candidate B receives 7 and candidate A 6 votes. Result of the election: C before B before A. However, this method is not a preferred option.

Some properties and uses

The restrictions of Arrow's impossibility theorem or Gibbard-Satterthwaite theorem apply to all methods of the preferred choice . In addition, each process has its individual advantages and disadvantages.

Politically, the preferential election in the form of the IRV is used, for example, as representative election in Australia and Ireland. The winner of the Eurovision Song Contest is determined by a special form of Borda election.

See also

Social choice theory

source

The big Eichborn: Wirtschaftswoerterbuch, Vol. 1: English - German, 3rd edition 2003, ISBN 3-921392-26-8 , p. 1001