Variants on Instant Runoff

A practical view

There’s a deep and technical literature on ways of evaluating algorithms for picking the winner of ranked choice ballots. It needs to be said that especially for cases where there’s only a single winner most of the time all the algorithms give the same answer. Ranked choice ballots are so clearly superior that getting them adopted at all, regardless of the algorithm, is much more important than getting the exact algorithm right. To that end instant runoff has the brand and is the most widely used because, quite simply, people understand it.

In case you don’t know, instant runoff is meant to do what would happen if a runoff election would take place but it happens, well, instantly. Technically (well, not so technically) that algorithm isn’t literally used. That algorithm would involve eliminating all candidates except the top two first place vote getters and then running a two way race between them on the ballots. That algorithm is obviously stupid, so what’s done instead is the candidate who gets the fewest first place votes is eliminated and the process is repeated until there’s only one candidate left. So there’s already precedent for using the term ‘Instant Runoff’ to refer to ranked ballot algorithms in general and swapping out the actual algorithm for something better.

There’s a problem with instant runoff as commonly implemented which is a real issue and is something the general public can get behind. If there’s a candidate which is listed second on almost everyone’s ballots then they’ll be the one eliminated first even though the voters would prefer them over all other candidates. Obviously this is a bad thing. The straightforward fix for this problem is to simply elect the candidate who would win in a two-way race against all other candidates, known as the condorcet winner. This is easy to explain but has one extremely frustrating stupid little problem: There isn’t always a single such candidate. Such scenarios are thankfully rare but unfortunately the algorithms proposed for dealing with them tend to be very technical and hard to understand and result in scaring people into sticking with instant runoff.

As a practical matter, the improved algorithm which would be bar far the easiest to get adopted would be this one: If there’s a single Condorcet winner they win. If not then the candidate with the fewest first place votes is eliminated and the process is repeated. This is easy enough to understand that politicians won’t be scared by it and in every case it either gives the same answer as the standard instand runoff or a clearly superior one, so it’s clearly superior with no real downsides.

This algorithm also has the benefit that it may be objectively the best algorithm. If the more technical methods of selecting a winner are used then there’s a lot of subtle gaming which can be done by rearranging down-ballot preferences to make a preferred candidate win, including insidious strategies where a situation where there is no single Condorcet winner are generated on purpose to make the algorithm do something wonky. Looking only at top votes minimizes the amount of information used hence reducing potential gaming potential and also maximizes the damage votes are doing to their own ballot if they’re trying to play games. In this case the general voter’s intuitions that complex algorithms are scary and top votes are very important are good ones.