I derive the probability that a vote cast in an Instant Runoff Voting election will change the election winner. I phrase that probability in terms of the candidates' expected vote totals, and then I estimate its magnitude for different distributions of voter preferences. The result is very similar to the probability of casting a pivotal vote in a Single-Member District Plurality election, which suggests that Instant Runoff Voting does not actually increase or decrease voters' incentives to vote strategically. The derivation uncovers a counter-intuitive phenomenon that I call "indirect pivotality", in which a voter can cause one candidate to win by ranking some other candidate on their ballot.

翻译：我推导了在即时 runoff 投票选举中，一票改变选举获胜者的概率。我将该概率表述为候选人预期得票总数的函数，然后针对不同的选民偏好分布估计其大小。结果与单一选区相对多数选举中投出关键一票的概率非常相似，这表明即时 runoff 投票实际上并不会增加或减少选民进行策略性投票的动机。推导过程揭示了一种反直觉的现象，我称之为“间接关键性”，即选民可以通过在选票上对某位候选人进行排序，从而使得另一位候选人获胜。