The Tideman Alternative method, also called Alternative- Smith voting, is a voting rule developed by

Nicolaus Tideman Thorwald Nicolaus Tideman (, not ; born August 11, 1943, in Chicago, Illinois) is a Georgist economist and professor at Virginia Tech. He received his Bachelor of Arts in economics and mathematics from Reed College in 1965 and his PhD in economics ...

which selects a single winner using

ranked ballots Ranked voting is any voting system that uses voters' Ordinal utility, rankings of candidates to choose a single winner or multiple winners. More formally, a ranked vote system depends only on voters' total order, order of preference of the cand ...

. This method is Smith-efficient, making it a

Condorcet method A Condorcet method (; ) is an election method that elects the candidate who wins a majority of the vote in every head-to-head election against each of the other candidates, whenever there is such a candidate. A candidate with this property, the ...

, and uses the

alternative vote Instant-runoff voting (IRV; ranked-choice voting (RCV), preferential voting, alternative vote) is a single-winner ranked voting election system where one or more eliminations are used to simulate runoff elections. When no candidate has a ...

( RCV) to resolve any cyclic ties.

Procedure

The procedure for Tideman's rule is as follows: # Eliminate all candidates who are not in the top cycle (most often defined as the

Smith set The Smith set, sometimes called the top-cycle or Condorcet winning set, generalizes the idea of a Condorcet winner to cases where no such winner exists. It does so by allowing cycles of candidates to be treated jointly, as if they were a single C ...

). # If there is more than one candidate remaining, eliminate the candidate ranked first by the fewest voters. # Repeat the procedure until there is a

Condorcet winner A Condorcet winner (, ) is a candidate who would receive the support of more than half of the electorate in a one-on-one race against any one of their opponents. Voting systems where a majority winner will always win are said to satisfy the Condo ...

, at which point the Condorcet winner is elected. The procedure can also be applied using tournament sets other than the Smith set, e.g. the

Landau set In the study of electoral systems, the uncovered set (also called the Landau set or the Fishburn set) is a set of candidates that generalizes the notion of a Condorcet winner whenever there is a Condorcet paradox. The Landau set can be thought of ...

Copeland set The Copeland or Llull method is a ranked-choice voting system based on counting each candidate's pairwise wins and losses. In the system, voters rank candidates from best to worst on their ballot. Candidates then compete in a round-robin tourna ...

, or

bipartisan set Bipartisanship, sometimes referred to as nonpartisanship, is a political situation, usually in the context of a two-party system (especially those of the United States and some other western countries), in which opposing political parties find co ...

Features

Strategy-resistance

Tideman's Alternative strongly resists both

strategic nomination Strategic nomination refers to the entry of a candidate into an election with the intention of changing the ranking of other candidates. The name is an echo of ‘tactical voting’ and is intended to imply that it is the candidates rather than the ...

and

strategic voting Strategic or tactical voting is voting in consideration of possible ballots cast by other voters in order to maximize one's satisfaction with the election's results. Gibbard's theorem shows that no voting system has a single "always-best" strat ...

by political parties or coalitions (although like every system, it can still be manipulated in some situations). The Smith and runoff components of the system each cover the other's weaknesses: # Smith-efficient methods are difficult for any coalition to manipulate, because no majority-strength coalition will have an incentive to remove a Condorcet winner: if most voters prefer A to B, A can ''already'' defeat B. #* This reasoning does not apply to situations with a

Condorcet cycle In social choice theory, Condorcet's voting paradox is a fundamental discovery by the Marquis de Condorcet that majority rule is inherently self-contradictory. The result implies that it is logically impossible for any voting system to guarante ...

, however. #* While Condorcet cycles are rare in practice with honest voters,

burial Burial, also known as interment or inhumation, is a method of final disposition whereby a dead body is placed into the ground, sometimes with objects. This is usually accomplished by excavating a pit or trench, placing the deceased and objec ...

(ranking a strong rival last, below weak opponents) can often be used to manufacture a false cycle. #

Instant runoff voting Instant-runoff voting (IRV; ranked-choice voting (RCV), preferential voting, alternative vote) is a single-winner ranked voting election system where one or more eliminations are used to simulate runoff elections. When no candidate has a ...

is resistant to burial, because it is only based on each voter's top preference in any given round. This means that burial strategies effective against the Smith-elimination step are not effective against the instant runoff step. #* On the other hand, instant-runoff voting is highly vulnerable to compromising strategy, where voters are incentivized to rank "lesser evils" higher in order to defeat a "greater evil". #* However, if a Condorcet winner exists, they're immune to compromising, so electing them reduces compromise incentive. The combination of these two methods creates a highly strategy-resistant system.

Spoiler effects

Tideman's Alternative fails

independence of irrelevant alternatives Independence of irrelevant alternatives (IIA) is an axiom of decision theory which codifies the intuition that a choice between A and B (which are both related) should not depend on the quality of a third, unrelated outcome C. There are several dif ...

, meaning it can sometimes be affected by spoiler candidates. However, the method adheres to a weaker property that eliminates most spoilers, sometimes called

independence of Smith-dominated alternatives Independence of Smith-dominated alternatives (ISDA, also known as Smith- IIA) is a voting system criterion which says that the winner of an election should not be affected by candidates who are not in the Smith set. Another way of defining ISDA i ...

(ISDA). This method states that if one candidate (X) wins an election, and a new alternative (Y) is added, X will still win the election as long as Y is not in the highest-ranked cycle.

Comparison table

The following table compares Tideman's Alternative with other single-winner election methods:

References

* Green-Armytage, James
Four Condorcet-Hare Hybrid Methods for Single-Winner Elections
{{voting systems Single-winner electoral systems