Strategy-Free Elections, And The True Measure of a Voting System

If you get involved in the debate on voting system reform, it's never long before someone brings up the concept of "strategic voting." The idea is simple enough: we all want to be as honest as possible on our ballots, but because the voting system is imperfect, we vote otherwise. This is easy to see in plurality; lots of people who claim to really want a third-party candidate end up voting for one of the two major-party candidates on election day. But it happens, to a lesser or greater extent, under all voting methods.

Actually, that's a cleverly-constructed lie of omission.

It turns out that there are a number of voting systems which are 100% strategy-free, so your honest vote will always also be your best vote. But you're not going to like them. Here's an example: voting is performed like plurality, i.e., each voter picks a single candidate. The winner is whichever candidate is named on a ballot chosen at random. Clearly, you should always vote the one candidate you think is best for the job, because there's no reason to fear that you're "throwing your vote away" or making it easier for a candidate you dislike to win. The clever part in the constructing of the lie was omitting the word deterministic, which means "no random components". There are no strategy-free deterministic voting systems.

Constructing other (and better) strategy-free methods is easy enough. So if strategy is so vitally important that it invariably comes up in every voting-system discussion, why don't we use one of them? The answer is: average performance. Random ballot voting, as your intuition probably tells you, is an absolutely terrible system. But intuition is sometimes wrong, so it's important that we can back it up with data by running computer simulations to calculate Bayesian regret. And the data shows that, based on the number of candidates competing, random ballot is two- to four-times worse than plurality voting; which we all know from experience to be a pretty bad system.

Strategy, and a voting system's susceptibility to it, are an important thing to be aware of. But immunity to strategy, even though it sounds like a great thing to strive for, isn't the goal of a voting system; if it were, we'd have an easy answer to the problem, in the form of non-deterministic voting methods. And there are a host of other reasonable-sounding things for a voting system to accomplish, many of which have been codified as voting system criterion. But, besides many of them being mutually-exclusive (i.e., you can't meet them all), using any of them as a litmus test obscures the true objective, in the same way that focusing exclusively on being strategy-free obscures the true objective. The only true measure of a voting system is it's expected performance: how well it delivers a desirable candidate to the electorate. Average performance, as measured by Bayesian regret, smooths over all the coarse edges of criterion, implicitly assessing all of them for frequency as well as impact.

Why should it matter that, for instance, approval voting fails the majority criteria, if the failure rate is vanishingly-infrequent and has minimal impact? When it performs significantly better than a host of other systems that do meet this criteria, but fail some other, equally-reasonable criteria? It shouldn't. Holding the percentage of strategic voters constant, approval voting has significantly better performance than just about any other voting method. Range voting (AKA score voting) can be even better. Which criteria are passed are secondary to that fact.

What Do You Mean By "Best"?

Plurality voting is terrible and should be replaced, but what's the best voting system to replace it with? This isn't a new revelation, or a new question; for instance Thomas Jefferson considered the problem. But academic inquiries to it had been in a lull since Kenneth Arrow's Nobel-prize-winning work in 1950 showed that, given certain assumptions, there was no perfect system. Social-decision scientists everywhere were crushed.

What little debate that continued about the subject focused around various "voting system criteria". Arrow's work had shown that a group of five certain "clearly necessary" criteria were mutually exclusive, but perhaps by breaking certain ones in a minimally-damaging way an almost-perfect voting system could be found. The problem was, no one could agree which criteria were most important; each practitioner could always come up with some worst-case scenario in which their opponents latest new proposal clearly gave a horrible result (usually involving a candidate named "Hitler" winning the election, just to make the point clear.) And so the debate degenerated to what situations were more likely to come up or led to more damaging results: the terrible one I concocted for your new voting system, or the terrible one you concocted for mine. But all these arguments lacked one important piece: evidence.

To make good estimates of how often various worst-case scenarios happen and how bad they are, it would take at least hundreds of elections, each with a minimum of a few hundred participants, multiplied by each of dozens of systems that had been developed, in order to get a clear picture. But even then, what do you measure? When your experiment is to ask people "what's the best ice-cream favor," how do you measure whether the voting system was right without knowing the right answer ahead of time? And how would you determine the right answer ahead of time, without asking people to vote on it?

The problem is that economic utility can't be measured directly. Combined with the in-feasibility of performing enough test-elections, it's enough to make almost anyone throw up their hands in frustration.

But here's a clever idea: what if we replace real people with little bits of computer code? Instead of futilely trying to measure each participants utility, we can just assign them randomly from a statistical distribution. We'll have each little bit of code "vote" using every one of the electoral methods we've developed, but also calculate what the maximum possible utility could be from each election, and see how much we miss by. And we'll do it a few hundred times and take the average. Running the whole simulation should take maybe a long weekend. (If only Arrow had had access to a modern desktop computer!) What would we find? Let's ask Professor Warren D. Smith, who ran this simulation over the 1999/2000 New Year's holiday.

If the data from this simulation is to be believed, using approval voting, or score voting (listed here as range voting), could improve the results of our elections by the same proportion as voting at all is an improvement over choosing our leaders at random. That's an astounding result!

Of course, there are still critics: most of them just repeat their favorite criteria argument (usually later-no-harm or majority, since score and approval fail them) ignoring that this data already accounts for any downsides from those short-comings. A few smug folks point out that you can't measure utility; but we already know that, that's why we used a simulation. Some attacked the statistical distribution of utility (now we're getting to something meaty!), so a series of better distributions, based on their suggestions, were used: the results were virtually the same. Then they argued that voters are a poor judge of their own utility; so the experiment was rerun with a "voter uncertainty" parameter. Even with a 50% error factor, score and approval still top the list.

The most bizarre argument is that score and approval can't be the best voting systems, because they aren't voting systems at all. You see, one of Arrow's assumptions was that a voting system would convert a set of all voter's "ranked-order preferences" into a societal order of ranked preferences. But score and approval don't used ranked-order preferences; perhaps, if Arrow hadn't used this overly-restrictive requirement, it wouldn't have taken 50 years to find these results.

Not only is this an astounding result, it seems to be a fairly unassailable result. The "best" voting system is score voting, and approval is almost as good (but easier to implement).