Strategic Behavior is Bliss: Iterative Voting Improves Social Welfare

Joshua Kavner, Lirong Xia

Published 2021-06-16Version 1

Recent work in iterative voting has defined the difference in social welfare between the truthful winner and worst-case equilibrium winner, due to repeated strategic manipulations, known as the additive dynamic price of anarchy (ADPoA). While all iterative plurality winners have been shown to differ from truth by at most one initial vote, it is less understood how agents' welfare changes in equilibrium. To this end, we differentiate agents' utility from their iteration mechanism and determine iterative plurality's ADPoA in the worst- and average-case. We first negatively demonstrate that the worst-case ADPoA is linear in the number of agents. In expectation, rather, equilibrium winners have a constant order welfare advantage over the truthful winner. Our positive results illustrate the prospect for social welfare to increase due to strategic manipulation.