Quick Runoff: Difference between revisions

 

The method is so named because in the three-candidate case it is not as "instant" as [[IRV]], as instead of a single top-two runoff, there is first a simulated runoff between the top two candidates, and then potentially the bottom two candidates.

 

The method may be badly named because the winner is actually found without doing any vote transfers. The results of the "runoffs" are inferred from the pairwise contests.

 

==Definition==

QR satisfies [[Later-no-harm]] because if candidate X is elected, the addition of a lower preference can only cause X to lose if it creates a majority defeat of X by the candidate that follows X in descending first preference order. This cannot be done by a voter who prefers X to the new preference.

 

 

QR also doesn't satisfy [[Later-no-help]]. In particular, in a three candidate scenario where A has the most first preferences and C the fewest, C may have incentive to insincerely create a majority win for B over A, if the C voters believe C has the second-preferences of the A voters. So, while the A voters technically have both Later-no-harm and Later-no-help guarantees with respect to A, there may be an incentive to withhold their second preference if they feel other factions are relying on those second preferences in order to try to steal the race from A.

Note that the supporters of the top two candidates (by first preferences) have both [[Later-no-harm]] and [[Later-no-help]] assurances. Labeling the candidates A, B, and C, the A voters' lower preference is only counted once A is known to have lost. The B voters' lower preference is not regarded at all, because candidates are only compared to their "adjacent" candidates in first-preference order, and A vs. C (the race that B voters can influence) are not adjacent.