It seems to be common wisdom among economists that voting is irrational, on the grounds that you are extremely unlikely to be the deciding vote. I don’t think this is the right way of looking at it. Obviously, if you knew how everyone else was voting, then you could decide whether or not your vote was needed beforehand. But us mere mortals will, I think, have to stick to Bayesian analysis. Before the votes are counted, you have some estimate of the probability that your side will win. Every vote you know about updates this probability – even if there are millions of votes. If you friend tells you he is voting Obama, and you didn’t already know that, then you must consider an Obama victory to be ever-so-slightly more likely than before. And the same analysis applies to your own vote. If the probability of an Obama victory is, in your estimate, X without your vote, then it must be X+epsilon after you factor in your vote. A small epsilon, perhaps, but not zero! If you think that increasing your side’s chance of victory by epsilon is worth standing in line for two hours, then it is quite rational to vote. This binary stuff is for computers; even voters – notoriously a bunch of sheep – can do better than that.

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You’re technically right that epsilon>0 but it should be added that it’s not a uniform constant, it *depends* highly on one’s current estimate of the likely outcome. After all it’s essentially the derivative of a sigmoid function, i.e. sort of a smoothed-out delta function. Thus it will vary by orders of magnitude between folks who live in Ohio v. folks who live in, say, New York or Texas. Yet the ‘standing in line for two hours’ cost part is more or less constant. The result is that your argument works far more often for people who live in “swing states” than those who live in “safe states”, for whom there is essentially no reason to vote whatsoever (regardless of which candidate they prefer).

But people who live in “swing states”, and know it, and are interested in politics, were going to vote anyway.

Hum. It seems to me that people are willing to spend the two hours even for the epsilon you get in a non-swing state. (After all, if nobody voted, then one vote would be decisive and it wouldn’t be non-swing.) So by revealed preference, that epsilon is worth the two hours. Plus of course you get a bunch of signalling effects.

Of course people are willing to vote. The claim is that they are irrational, i.e. the cost is greater than the objective payoff (influencing an election outcome by epsilon). The fact that people vote doesn’t ‘reveal’ that the epsilon is worth the cost. It could just be – indeed, probably is – that the payoff people perceive from voting is based on something other than the objective influence their vote has on the election.