Sincere-strategy preference-based approval voting broadly resists control

Abstract

We study sincere-strategy preference-based approval voting (SP-AV), a system proposed by Brams and Sanver [8], with respect to procedural control. In such control scenarios, an external agent seeks to change the outcome of an election via actions such as adding/deleting/partitioning either candidates or voters. SP-AV combines the voters' preference rankings with their approvals of candidates, and we adapt it here so as to keep its useful features with respect to approval strategies even in the presence of control actions. We prove that this system is computationally resistant (i.e., the corresponding control problems are np-hard) to at least 16 out of 20 types of constructive and destructive control. Thus, for the 20 control types studied here, SP-AV has more resistances to control, by at least two, than is currently known for any other natural voting system with a polynomial-time winner problem. © 2008 Springer-Verlag Berlin Heidelberg.