NP-Hard Manipulations of Voting Schemes

Voting schemes are common social choice function that allow voters to aggregate their preferences in a socially desirable way. Unfortunately, the GibbardSatterthwaite theorem states that many of these schemes are susceptible to manipulation. Thus, a highly desirable quality, such that a scheme is resistant to manipulaion, is lacking in voting schemes. Since non-manipulability cannot be guaranteed, researchers have investigated other ways to discourage manipulation. This research has led in the direction of voting schemes which are difficult to manipulate. The investigation of these schemes has greater importance in the area of multiagent systems. In this case, voters are computer agents who can determine strategic voting schemes much quicker than their human counterparts. Thus, having voting schemes which are computationally difficult to manipulate is a desirable quality in these settings.