Inefficiency-Manipulability Tradeoff in the Parallel Mechanism

Abstract

Most school choice and other matching mechanisms are based on deferred acceptance (DA) for its incentive properties. However, non-strategyproof mechanisms can dominate DA in welfare because manipulation in preference rankings can reflect the intensities of underlying cardinal preferences. In this work, we use the parallel mechanism of Chen and Kesten, which interpolates between Boston mechanism and DA, to quantify this tradeoff. While it is previously known that mechanisms that are closer to Boston mechanism are more manipulable, we show that they are also more efficient in student welfare if school priorities are weak. Our theoretical results show the inefficiency-manipulability tradeoff in the worst case, while our simulation results show the same tradeoff in the typical case.