In elections, Strategic Voting, also known as tactical or insincere voting, occurs when some voters cast ballots that do not reflect their sincere preferences in the hope that such a vote will obtain a better outcome. Because The Equal Vote Coalition promotes Honesty as among our core criteria for voting method efficacy, a look at what strategic incentives are created by various voting methods is key to determining their viability for contested public elections. Stated again, the first of our five voting method critera is defined as follows:
Honesty: Can the voter safely express her honest opinion on the ballot, and likewise, to what level does the system disincentivize voters from strategically voting insincerely in order to produce a better outcome?
There are four distinct types of insincere voting that are possible in rated and ranked voting systems:
A choice is strongly insincere if the voter offers a higher level of support to at least one candidate than that offered to his or her most preferred candidate. In keeping with the seriousness of this offense, the authors of this paper call it "decapitation"; other sources call it "compromising." In more modern parlance, this is known as Favorite Betrayal.
The incentive for strong insincerity is amonst the very critical defects of our current "support only one" voting method. If your true favorite candidate is not one of the two frontrunners in the election, there is a strong incentive to tactically support the one of those two the voter finds least distasteful (i.e. the "lesser evil") rather than "wasting the vote" on a "spoiler" candidate.
Despite the claims of the method's advocates, strong insincerity can also be incentivized under RCV/IRV. The following video demonstrates how strong insincerity can come into play if the voter isn't sure that her true favorite is either a very strong nor a very weak candidate:
FairVote's article on Australian IRV elections confirms that savvy voters cast, and major political parties encourage, strongly insincere ballots.
STAR Voting never encourages strong insincerity in balloting. In order for an honest vote of maximum support for a true favorite to create a worse outcome for the voter under STAR, that support would have to knock a more viable "lesser evil" out of the automatic runoff. Because viability is highly correlated with overall score, a voter who fears her favorite and "lesser evil" are vying for second position in the runoff will be highly motivated to send the stronger of the two to the runoff in order to have the best chance of defeating the greater evil.
Weak Insincerity is also known as "burying" or "skipping." A vote is weakly insincere if includes offering maximum support amongst the choices to the voter's most preferred candidate, but skips support for a less preffered candidate in favor of candidates even less preferred. Voting methods including the Borda Count are vulnerable weak insincerity.
Although FairVote has hypothesized that voters will be tactically incentived to "bury" a strong consensus candidate, this analysis does not hold up to reasonable scrutiny. The reality is that under STAR, voters are only likely to promote other challengers they like more than that strong consensus choice for a very simple reason: promoting any other candidate the voter likes less over a strong consensus choice increases the likelihood that the voter's first choice will get squeezed out of the runoff. And should that happen, the voter's full runoff vote will go to the least-preferred candidate. Should multiple factions adopt this strategy as FairVote suggest would have happened in a recent French election, all but one faction would see a worse outcome than had they voted sincerely. No voting system prevents voters from trying to be sneaky, but STAR Voting does a great job of giving no advantage for it.
"The Effect of Approval Balloting on Strategic Voting Under Alternative Decision Rules" confirms this conclusion, suggesting that burying is only effective in a multistage score process if the voter holds three key beliefs, (1) and (2) with great confidence: (1) that his favorite can make the runoff, (2) that his favorite can beat a third or lower preference candidate, (3) and that he is not sure his favorite can beat his second favorite in the runoff. Under STAR Voting, the voter who believes (3) cannot believe (1) with great confidence: if you aren't sure your favorite can beat your second choice, your first choice is in play for the second spot in the runoff. Adding any support to a less preferred candidate in this scenario simply increases the likelihood your own favorite will be squeezed out and that your runoff vote will go to someone you really don't like.
Restrictive sincerity, also known as Tactical Minimization or "truncation," is where you decrease your support for some candidates other than your favorite. Pure Approval and Score voting systems are said to encourage tactical "bullet voting" - supporting just one's favorite candidate and dishonestly voting 0 for all the others in order to give the favored candidate the best chance of winning.
STAR Voting's runoff step corrects for strategic restrictive sincerity in two ways: first, by incentivizing voters to differentiate scores of multiple candidates to have a meaningful say in the runoff, and by equalizing the outcome influence of all voters in the runoff step.
A choice is expansively sincere if the voter offers higher support for secondary choices than would otherwise constitute a truly sincere vote. The extreme of expansive sincerity, Tactical Maximization, is where you increase support for candidates other than your favorite because you think your favorite is weak or you want to hedge your bet. In addition to the folks who say Score Voting systems are vulnerable to strategic "bullet voting", there are those who say the optimal Score vote is pretty much the opposite: that voters will gain strategic advantage by maximizing support for one perceived front runner and all the candidates the voter likes more than that one.
As above, STAR Voting's runoff step corrects for this strategic distortion in two ways: first, by incentivizing voters to differentiate scores of multiple candidates to have a meaningful say in the runoff, which amplifies the voice of those who do not maximally vote the top two into the runoff step.
While no voting system entirely eliminates the tendency for voters to try to "game the system", STAR Voting both minimizes tactical voting and corrects for its distortion in the runoff step. This tendency to correct for scoring distortion explains in large part why STAR Voting performs exceedingly well in election method simulation with both honest and tactical voters.