Incentive ratio: a game theoretical analysis of market equilibria

In a Fisher market, the market maker sells m products to n potential agents. The agents submit their utility functions and money endowments to the market maker, who, upon receiving submitted information, derives market equilibrium prices and allocations of the products. Agents are self-interested entities who wish to maximize their utility, and they may misreport their private information for this purpose. The incentive ratio characterizes the extent to which strategic plays can increase an agent's utility. While agents do benefit by misreporting their private information, we show that the ratio of improvement by a unilateral strategic play is no more than two in markets with gross substitute utilities for the agents. Moreover, it can be pinned down to e 1/e≈1.445 in Cobb-Douglas markets. For the Leontief markets in which products are complementary, we show that the incentive ratio is at most two as well.