Strategy-resistance Tideman's Alternative strongly resists both
strategic nomination and
strategic voting 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, however. • While Condorcet cycles are rare in practice with honest voters,
burial (ranking a strong rival last, below weak opponents) can often be used to manufacture a false cycle. •
Instant runoff voting 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, 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 (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 ==