But we maximize our utility expectation, or that of our descendants or relatives, in that future election if we advocate a voting system that does very well by social utility, the sum of the voters' utilities.
That's a good reason to judge methods by SU, and I claim that it's completely compellling.
I think there is a need for SU as a standard, but wish I could find a rock-solid justification for translating unbounded individual utilities to a common scale before summing them, as is commonly done. It seems useful to do so, since it's close to what an election method does anyway, but technically your future expectation should be maximized by summing the *unbounded* utilities (at least if all voters are equally likely to have extreme utilities some time in the future).
If distances in issue-space are measured by city-block distance, then the CW always maximizes SU in spatial models.
If distance in issue-space is measured by Euclidean distance, then the CW maximizes SU under the conditions assumed in all spatial simulations.
If, for any line through come central point in issue space, the voter population density distribution is the same in both directions along that line from the central point, then, even with Euclidean distance, the CW maximizes SU.
The condition in the above paragraph is met, for instance, if the voters are normally distributed about a central point in each issue dimension, as is routinely assumed in spatial model simulations.
This doesn't seem possible for more than one dimension-- don't Merrill's models show sincere Borda yeilding slightly higher SU than the CW in two dimensions, and Approval higher than both when there are only three candidates?
Bart ---- Election-methods mailing list - see http://electorama.com/em for list info
