Social choice theory analyzes a decision between a collection of alternatives made by a collection of 
voters with separate opinions. Any choice for the entire group should reflect the
desires of the individual voters to the extent possible.
The metric voting distortion of a voting rule measures its worst-case loss in social cost when the underlying metric is unknown and only the voters' rankings are available.
Fair choice procedures usually satisfy anonymity (invariance under permutation of voters), duality (each alternative
receives equal weight for a single vote), and monotonicity
(a change favorable for 
does not hurt 
). Simple majority vote is anonymous, dual, and monotone. May's theorem states a stronger result.
