"Favorite Betrayal" – Executive Summary

An election is said to exhibit "favorite betrayal" if some set of voters would have gotten a better election result ("better" in their view) by not voting their honest favorite top. A voting method enjoys the "FBC property" if no election (with that voting method) exhibits favote betrayal.

We've come a long way since the days when range and approval voting were the only known methods in which betraying your favorite is strategically avoidable. Now many other methods also are known with that "FBC property." Many of them were invented by Kevin Venzke.

• However, it appears Range and Approval satisfy FBC in a stronger and more obvious sense than these other methods. Specifically, with Range and Approval, betraying your favorite simply never is useful. With the other methods it can be strategically useful (cause X to win instead of Y, where the betrayers prefer X) but if so there is always a way to get the same effect (i.e. make X win) by some other dishonest vote not involving favorite betrayal.
• Also, all the FBC-obeying methods surveyed seem vulnerable to candidate-cloning election-manipulation attempts except for range (and in a weaker sense approval) voting. This leads to the very interesting

Conjecture: Continuum Range Voting (and its obvious variants) are the only FBC-obeying voting methods immune to candidate-cloning (with voters assumed to have tiny preferences among the clones).

This conjecture has now been largely proven.

Detailed survey of FBC-compliant election methods

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