Wei_Dai comments on Arrow's Theorem is a Lie - Less Wrong

27 Post author: alyssavance 24 October 2009 08:46PM

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Comment author: taw 24 October 2009 09:24:18PM 12 points [-]

The procedure you're proposing collapses into approval voting immediately.

Nobody has any reason to vote anything else than 10 (possibly minus epsilon) or 0 (possibly plus epsilon). If you like A slightly more than B, and estimate A will get 81 points, while B will get 90 points, the optimal behaviour is to vote 10 for A (and everything better than A), and 0 for B (and everything worse than B), any other vote is strictly worse for you. There is no scenario under which voting anything else than 0 and 10 is better than extreme votes.

Approval voting is prone to tactical voting (this should added to requirements, Arrow's Theorem talks about preferences, as it assumes voting is uniquely determined by them) - you never need to order candidates in a way that reverses your preferences, but approval threshold depends on what you think others will vote like. If you think A > B > C, and think C is leading, you vote 10,10,0. If you think B is leading, you vote 10,0,0. It also fails at determinism.

If we give people predefined allowance of points (like n alternatives need scores 1 to n, or get n points for arbitrary distribution) it fails independence immediately, and is prone to preference reversal in tactical voting, which is even worse (if A > B > C, and C is leading, but B has some chances, you vote 0, 10, 0, with A < B).

Comment author: Wei_Dai 27 October 2009 03:06:37AM 2 points [-]

Relevant section from Steve Rayhawk's nursery effect link:

If an 0-99 range voter has given 0s and 99s to the candidates she considers most likely to win, and now asks herself "how should I score the remaining no-hope candidates?", the strategic payoff for exaggerating to give them 0s or 99s can easily be extremely small, because the probability of that causing or preventing them winning can easily be below 10^-100. Supposing a voter gets even a single molecule worth of "happiness neurotransmitter" from voting honestly on these candidates, that happiness-payoff is worth more to that voter than the expected payoff from exaggerating about these candidates via "approval style" range-voting. Therefore, range voters will often cast substantially-honest range votes, even those inclined to be "strategic."