Sincere Favorite criterion
The Sincere Favorite criterion is a criterion proposed by Kevin Venzke as an approximation and simplification of the Favorite Betrayal criterion. Sincere Favorite is a relative criterion defined on cast votes, whereas FBC is defined on sincere preferences and incentives.
It is assumed that the used election method permits the voter to tie any number of candidates in the top position. When this is not the case, as in standard Instant-runoff voting, it is simplest to say that Sincere Favorite is failed. Alternatively, one can require that the method satisfy the criterion when the candidates are given the top positions in an arbitrary order. This interpretation allows Random Ballot (with equal ranking disallowed) to comply.
Suppose a subset of the ballots, all identical, rank every candidate in S (where S contains at least two candidates) equal to each other, and above every other candidate. Then, arbitrarily lowering some candidate X from S on these ballots must not increase the probability that the winner comes from S.
Or more simply: The voter must not be able to help his favorite candidates by not voting for some of them.
Sincere Favorite is satisfied by Approval voting (and, e.g., range voting and median rating), MDDA, MAMPO, Minmax(pairwise opposition),Improved Condorcet Approval, ICT, and Symmetrical ICT. Most varieties of MCA satisfy the criterion. Other Minmax methods can be modified to satisfy it using the tied at the top rule.
If a voter believes there are situations under the used election method where giving his favorite candidate the top position may harm his compromise choice's chances of winning, even when the favorite and compromise are tied together in the top position, the voter might decide it is a safer strategy to not vote for his favorite candidate at all. In particular, the voter might make this decision when the favorite candidate is not expected to win the election.
Methods which satisfy Sincere Favorite never enable a voter to help his favorite candidates by not voting for one of them.