Pareto efficiency

The Pareto criterion is a basic criterion for evaluating voting systems. It can be defined in this way:

If every voter ranks candidate A above candidate B, then B must not be elected.

This criterion is important in the context of Arrow's impossibility theorem.

Virtually every devised election method satisfies this criterion. An example of a method which would fail it would be Random Candidate, where some candidate is elected at random, regardless of the submitted votes.