Monotone strategyproofness

We propose a way to compare the extent of preference misrepresentation between two strategies. We define a preference revelation mechanism to be monotone strategyproof if declaring a “more truthful” preference ordering dominates (with respect to the true preferences) declaring a “less truthful” preference ordering. Our main result states that a mechanism is strategyproof if, and only if, it is monotone strategyproof. This result holds for any deterministic social choice function on any domain; for probabilistic social choice functions it holds under a mild assumption on the domain.