Obvious dominance and random priority

Abstract

We characterize the full class of obviously strategy-proof mechanisms in environments without transfers as clinch-or-pass games that we call millipede games. Some millipede games are simple and widely used in practice, while others may be complex, requiring agents to perform lengthy backward induction, and are rarely observed. We introduce a natural strengthening of obvious strategy-proofness called strong obvious strategy-proofness, which eliminates these complex millipede games. We use our definition to characterize the well-known Random Priority mechanism as the unique mechanism that is efficient, fair, and simple to play, thereby explaining its popularity in practical applications.