Strategic nomination is the manipulation of an election

Election

An election is a formal decision-making process by which a population chooses an individual to hold public office. Elections have been the usual mechanism by which modern representative democracy operates since the 17th century. Elections may fill offices in the legislature, sometimes in the...

 through its candidate set (compare this to tactical voting

Tactical voting

In voting systems, tactical voting occurs, in elections with more than two viable candidates, when a voter supports a candidate other than his or her sincere preference in order to prevent an undesirable outcome.It has been shown by the Gibbard-Satterthwaite theorem that any voting method which is...

, where the manipulation comes from the voters). Strategic nomination is not to be confused with campaign strategy, the methods candidates employ in political campaign

Political campaign

A political campaign is an organized effort which seeks to influence the decision making process within a specific group. In democracies, political campaigns often refer to electoral campaigns, wherein representatives are chosen or referendums are decided...

s to win an election after nomination.

Independence of irrelevant alternatives

If the winner of an election were not running in the first place, then obviously someone else would have won instead. Similarly, if a candidate gets "added" to an election, it becomes possible for the new candidate to win. If these are the only cases in which a change in the candidate set leads to a different election outcome, then the voting system

Voting system

A voting system or electoral system is a method by which voters make a choice between options, often in an election or on a policy referendum....

 is independent of irrelevant alternatives and therefore immune to strategic nomination.

Independence of irrelevant alternatives, however, is a very hard property for a voting system to satisfy. This is illustrated by the following example of Condorcet's voting paradox

Voting paradox

The voting paradox is a situation noted by the Marquis de Condorcet in the late 18th century, in which collective preferences can be cyclic , even if the preferences of individual voters are not. This is paradoxical, because it means that majority wishes can be in conflict with each other...

:

• 40 voters preferring candidate A to B to C
• 35 voters preferring candidate B to C to A
• 25 voters preferring candidate C to A to B

With the above preferences and whatever candidate an election method chooses as a winner, another candidate can always secure a majority of votes against that winner by removing the third candidate. Since the absence of any candidate would leave the impression that the preference of the group of voters as a whole is a clear majority when by definition it is not when we consider the third candidate, one can argue that none of these candidates are actually "irrelevant."

The candidates in the example above form a cycle known as the Smith set

Smith set

In voting systems, the Smith set, named after John H. Smith, is the smallest non-empty set of candidates in a particular election such that each member beats every other candidate outside the set in a pairwise election. The Smith set provides one standard of optimal choice for an election outcome...

 - their combined presence provides conflicting information (both to the election system as well as to observers) about who the greatest candidate is. Strategic nomination, then, involves hiding this information from the voting system by excluding one of the candidates. Because of this strange relationship between the candidates and the voters, strategic nomination through this manner is doubtful as it becomes very much a question of whether the presence or absence in an election of a potential "cycle-maker" (provided one exists and can be found) can be decided by those who seek to gain from it.

Independence of clones

In order to simplify the issue, academic attention sometimes focuses on a specific kind of strategic nomination: the kind that involves clones. Clones in this context are candidates such that every voter ranks them the same relative to every other candidate, i.e. two clones of each other are never both strictly separated by a third member in the preference ranking of any voter, unless that member is also a fellow clone. Trivially, the set of all candidates makes up a clone set as does every subset consisting of one candidate. It thus makes no sense to just call a candidate a clone unless it is in the context of a clone set which contains at least two elements and is a proper subset of the set of all candidates.

It is desirable for the outcome of an election to be essentially unaffected by the addition or removal of clones. Adding or removing a clone candidate should only change the winner if the old winner, the new winner, and the candidate added or removed are all clones of each other. A voting system that satisfies this criterion is considered "independent of clones". Independence of clones was first formulated by Nicolaus Tideman

Nicolaus Tideman

T. Nicolaus Tideman is a Professor of Economics at Virginia Polytechnic Institute and State University. He received his Bachelor of Arts in economics and mathematics from Reed College in 1965 and his PhD in economics from the University of Chicago in 1969...

.

The existence of a true clone set in a public election is improbable, as it only takes one voter to break up a clone set. As a result of this fact, some argue that the independence of clones criterion has limited relevance to real-world elections. This criterion is still used in academic analysis, however, as many voting systems behave similarly when handling both clones and closely affiliated candidates with common supporters.

Types of strategic nomination

1. Vote-splitting happens when adding similar or clone candidates decreases the chance of any of them winning, also known as a spoiler effect
   Spoiler effect
   The spoiler effect describes the effect a minor party candidate with little chance of winning has in a close election, when that candidate's presence in the election draws votes from a major candidate similar to them, thereby causing a candidate dissimilar to them to win the election...
   
   . Methods that are vulnerable to this include the plurality
   Plurality voting system
   The plurality voting system is a single-winner voting system often used to elect executive officers or to elect members of a legislative assembly which is based on single-member constituencies...
   
    voting system and two-round runoff voting
   Two-round system
   The two-round system is a voting system used to elect a single winner where the voter casts a single vote for their chosen candidate...
   
   .
2. Teaming happens when adding more candidates actually helps the chances of any of them winning, as can occur in Borda count
   Borda count
   The Borda count is a single-winner election method in which voters rank candidates in order of preference. The Borda count determines the winner of an election by giving each candidate a certain number of points corresponding to the position in which he or she is ranked by each voter. Once all...
   
   s.
3. Crowding happens when adding candidates affects the outcome of an election without either helping or harming the chances of their factional group, but instead affecting another group. This can occur in Copeland's method
   Copeland's method
   Copeland's method or Copeland's pairwise aggregation method is a Condorcet method in which candidates are ordered by the number of pairwise victories, minus the number of pairwise defeats....
   
   .

External links

• Independence from similar alternatives Article by Stephen Eppley