The odds that your vote will actually affect the outcome of a given election are very, very, very slim. This was documented by the economists Casey Mulligan and Charles Hunter, who analyzed more than 56,000 Congressional and state-legislative elections since 1898. For all the attention paid in the media to close elections, it turns out that they are exceedingly rare. The median margin of victory in the Congressional elections was 22 percent; in the state-legislature elections, it was 25 percent. Even in the closest elections, it is almost never the case that a single vote is pivotal. Of the more than 40,000 elections for state legislator that Mulligan and Hunter analyzed, comprising nearly 1 billion votes, only 7 elections were decided by a single vote, with 2 others tied. Of the more than 16,000 Congressional elections, in which many more people vote, only one election in the past 100 years -- a 1910 race in Buffalo -- was decided by a single vote.

But there is a more important point: the closer an election is, the more likely that its outcome will be taken out of the voters' hands -- most vividly exemplified, of course, by the 2000 presidential race. It is true that the outcome of that election came down to a handful of voters; but their names were Kennedy, O'Connor, Rehnquist, Scalia and Thomas. And it was only the votes they cast while wearing their robes that mattered, not the ones they may have cast in their home precincts.

Still, people do continue to vote, in the millions. Why? Here are three possibilities:

1. Perhaps we are just not very bright and therefore wrongly believe that our votes will affect the outcome.

2. Perhaps we vote in the same spirit in which we buy lottery tickets. After all, your chances of winning a lottery and of affecting an election are pretty similar. From a financial perspective, playing the lottery is a bad investment. But it's fun and relatively cheap: for the price of a ticket, you buy the right to fantasize how you'd spend the winnings -- much as you get to fantasize that your vote will have some impact on policy.

3. Perhaps we have been socialized into the voting-as-civic-duty idea, believing that it's a good thing for society if people vote, even if it's not particularly good for the individual. And thus we feel guilty for not voting.