Ryan Enos and Anthony Fowler find that most people vote to "receive extrinsic benefits from voting that are unrelated to the chances that their vote will actually matter":
Americans vastly overestimate the chances that their vote will make a difference. Our median respondent felt that there is a 1 in 1000 chance that their vote could change the outcome of a Presidential election, missing the true chance by a factor of 10,000. However, this dramatic overestimation does not explain the prevalence of turnout, because those who actually vote know that this probability is low. Over 40% of regular voters know that the chances of a pivotal vote are less than 1 in a million. Amazingly, turnout is negatively correlated with the perceived chances that one vote will make a differencemeaning the less likely you are to think your vote will actually matter, the more likely you are to vote.
... If forced to think about it, most voters know that they won’t change an election result; but they don’t care. They benefit from voting, regardless of the electoral outcome. Voters enjoy wearing stickers, expressing their views, fulfilling their civic obligation, and earning the right to complain. For them, that’s reason enough.
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