Bounded Incentives in Manipulating the Probabilistic Serial Rule

The Probabilistic Serial mechanism is well-known for its desirable fairness and efficiency properties. It is one of the most prominent protocols for the random assignment problem. However, Probabilistic Serial is not incentive-compatible, thereby these desirable properties only hold for the agents' declared preferences, rather than their genuine preferences. A substantial utility gain through strategic behaviors would trigger self-interested agents to manipulate the mechanism and would subvert the very foundation of adopting the mechanism in practice. In this paper, we characterize the extent to which an individual agent can increase its utility by strategic manipulation. We show that the incentive ratio of the mechanism is 3/2. That is, no agent can misreport its preferences such that its utility becomes more than 1.5 times of what it is when reports truthfully. This ratio is a worst-case guarantee by allowing an agent to have complete information about other agents' reports and to figure out the best response strategy even if it is computationally intractable in general. To complement this worst-case study, we further evaluate an agent's utility gain on average by experiments. The experiments show that an agent' incentive in manipulating the rule is very limited. These results shed some light on the robustness of Probabilistic Serial against strategic manipulation, which is one step further than knowing that it is not incentive-compatible.

Interacting processes in phonological theory

This article introduces basic principles of a generative theory of phonology that unifies aspects of parallel constraint-based theories and serial rule-based theories. In the core of the grammar are phonological processes that consist of a markedness constraint and a repair. Processes are universal, but every language activates a different set, and applies them in different orders. Phonological processes may be in bleeding or feeding relations. These two basic relations are sufficient to define more complicated interactions, such as blocking, derived and non-derived environment effects, chain shifts and allophony.