[EM] DMC strategy

Simmons, Forest simmonfo at up.edu
Fri Sep 16 10:07:12 PDT 2005

Recently Rob Lanphier asked how to determine the strategically optimal approval cutoff when voting under DMC.
Here are my suggestions:
(1) For the case where you have enough polling information to discern the Smith set: 
First identify (with the letter  C) your favorite member of the Smith set (or, if possible, the uncovered set).
Put your approval cutoff just below the best Smith (or uncovered) candidate that cannot beat C pairwise. [In a Smith set with fewer than four members, all Smith members are uncovered.]
(2) For the zero information case:  Approve all of the candidates that you actually like.
Note that it never helps strategically to approve a non-Smith candidate, because such a candidate cannot doubly defeat a Smith candidate, and the DMC winner will always come from the Smith set.
By the same token, it never hurts to approve a non-Smith candidate if you really like her and want to show support.  This candidate will never get in the way of your Smith compromise candidate C.
It is useful to remember that DMC(Smith) will always give the same winner as plain DMC, assuming that approval cutoffs are not altered.
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