I was thinking about corporate elections today, and how under some voting systems an individual would want to strategically vote by submitting multiple, different ballots. I soon realized that this was generalizable to multiple voters with identical preferences in any election.
Basically, something like "If a group of voters share the same preferences, then their optimal strategy should be to vote in exactly the same way." Off the top of my head, there are a few systems that break this criterion: Single Non-Transferable Vote is one, as is limited block voting. In these instances voters of a sufficiently large group obviously need to spread out their votes a bit more. Borda also violates it - members of a large enough group will want to maximize their slate's points by "rotating" the list among them. I think multi-winner STV can break this in some ways, but I'm not sure when this occurs. This is interesting, as intuitively it seems like most PR methods should satisfy it (though perhaps in some cases with perfect information, due to anticipated rounding error). List PR could run into trouble too, especially list PR that overfavors smaller parties with an overly large divisor, however that seems only due to rounding error. What about other methods, though? Is there a single-winner election method that breaks this? Is there a divisor that prevents or minimizes this issue in List PR? Thanks, Scott Ritchie ---- election-methods mailing list - see http://electorama.com/em for list info