Abstract
We study a multi-dimensional collective decision under incomplete information. Agents have Euclidean preferences and vote by simple majority on each issue (dimension), yielding the coordinate-wise median. Judicious rotations of the orthogonal axes ñthe issues that are voted upon ñlead to welfare improvements. If the agentsí types are drawn from a distribution with independent marginals then, under weak conditions, voting on the original issues is not optimal. If the marginals are identical (but not necessarily independent), then voting Örst on the total sum and next on the di§erences is often welfare superior to voting on the original issues. We also provide various lower bounds on incentive e¢ ciency: in particular, if agentsítypes are drawn from a log-concave density with I.I.D. marginals, a second-best voting mechanism attains at least 88% of the Örst-best e¢ ciency. Finally, we generalize our method and some of our insights to preferences derived from distance functions based on inner products.