IRV Is Not Equivalent to Runoffs
Proponents of Instant Runoff Voting (IRV) often claim that it eliminates the need for runoff elections by giving an equivalent outcome. But the results are not always equal.
Different Outcomes with IRV & Runoffs
Here is a simple four-candidate election scenario which demonstrates that a runoff is not equivalent to IRV:
% of voters Their ranking
28% W > others
27% X > Y > others
23% Y > Z > others
22% Z > Y > others
With IRV, Z is eliminated, transferring 22% to Y, who then has 45%. X is then eliminated, transferring 27% to Y. Y then wins by 72% to 28%.
With a runoff, W and X go to the next round, with 28% and 27% respectively. So the winner is W, not X as was the case with IRV.
Further, many people like having the opportunity to focus on just two candidates, so they can get to know them better, and hopefully make a more informed decision than they could have with a more crowded slate. Thus, even when IRV and runoffs feature the same two candidates in the final round, they may bear different outcomes.