The paradox of voting, also called Downs paradox, is that for a rational, self-interested voter the costs of voting will normally exceed the expected benefits. Because the chance of exercising the pivotal vote (i.e. in case of a tied election) is tiny compared to any realistic estimate of the private individual benefits of the different possible outcomes, the expected benefits of voting are less than the costs. The fact that people do vote is a problem for public choice theory, first observed by Anthony Downs.[1]
Alternative responses modify the postulate of egoistic rationality in various ways. For example, Brennan and Lomasky suggest that voters derive 'expressive' benefits from supporting particular candidates. However, this implies that voting choices are unlikely to reflect the self-interest of voters, as is normally assumed in public choice theory; that is, rational behavior is restricted to the instrumental as opposed to the intrinsic value of actions.
Some have hypothesized that voting is linked genetically with evolved behaviors such as cooperation. One study of identical and fraternal twins' voting patterns concluded that 60% of differences in turnout among twins can be accounted for by genetics, but another interpretation of this study put the figure at 40%.[2]
Another suggestion is that voters are rational but not fully egoistic. In this view voters have some altruism, and perceive a benefit if others (or perhaps only others like them) are benefited. They care about others, even if they care about themselves more. Since an election affects many others, it could still be rational to cast a vote with only a small chance of affecting the outcome. This view makes testable predictions: that close elections will see higher turnout, and that a candidate who made a secret promise to pay a given voter if they win would sway that voter's vote less in large and/or important elections than in small and/or unimportant ones.