  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.
