There's a lot of argument over whether or not voting for a third party candidate is throwing your vote away. Most of the people arguing don't understand game theory because the only correct answer is, "It depends on your situation." While I know this my seem like a descent into politics, this is about the "game" behind voting systems in general. So here's my quick guide for optimal voting.
There's two ways to vote: for the short term outcome meaning who gets elected; and the long term outcome which is to attract the attention of political marketers. Most people are obsessed with the first and don't consider the second. Seth Godin has an excellent post on the later here. Voting for the short term outcome means voting for the better of the two leading candidates (or the lesser of two evils). Voting for the long term outcome means voting for the party that most closely matches your beliefs to let it be known what you really want. There's a large number of third parties in the U.S. that have more nuanced political views than the Republicans and Democrats. If a large number of voters are voting third party then one of the big two may change their stance on issues in order to win those voters over.
People like to claim that voting for long term outcomes is throwing your vote away but the big parties do change stances. If you look at the 1919 Senate vote on women's suffrage, the Republicans were mostly for it and the Democrats were split. Now, both parties support it because not to is suicide for a party. The parties don't care about the issues, they care about getting elected; the issues are a means to that end.
So when is voting for long term change not throwing your vote away?
- If your state isn't a swing state. (While this is not entirely true, not enough people care about Game Theory for this rule to hurt.)
- If you truly are opposed to both mainstream candidates.
- If you weren't planning on voting. (In which case you might also want to consider moving to another country. Please do us that favor.)
- Your state splits it's electoral votes proportionately to the popular vote. (currently no states do this, but I can dream, can't I?)
When is voting for a third party candidate throwing your vote away?
- If you live in a swing state. (every vote for the big two counts in these states)
- If you live in Maine or Nebraska, both of which split their electoral votes based on district.
In summary, vote for a mainstream candidate if you have a preference between the two in a race that will be close in your state. Vote with your beliefs if you have no preference or you're not likely to influence the vote.