Knowledge that Transforms

An effectivity function describes the blocking power of coalitions on subsets of alternatives. Given a preference profile, if any coalition blocks an alternative whenever it can, using its own power, make all of its members better off, only alternatives in the core can be reached. In this paper we study the incentives of the coalitions to use this power truthfully, i.e. to not manipulate. Some well known cores, among them the core of an exchange economy, are manipulable. We give sufficient conditions on an effectivity function that assure its core is nonmanipulable.

Sequential equilibria comprise consistent beliefs and a sequentially ra tional strategy profile. Consistent beliefs are limits of Bayes ratio nal beliefs for sequences of strategies that approach the equilibrium strategy. Beliefs are structurally consistent if they are rationaliz ed by some single conjecture concerning opponents' strategies. Consis tent beliefs are not necessarily structurally consistent, notwithstan ding a claim by Kreps and Robert Wilson (1982). Moreover, the spirit of structural consistency conflicts with that of sequential rationali ty. One avoids these difficulties by weakening structural consistency to allow convex combinations of opponents' strategies, but this intr oduces correlation into the strategies that justify out-of-equilibriu m beliefs. Copyright 1987 by The Econometric Society.

A structural consumption model incorporating endogenous liquidity constraints is fit to a cross section of 798 U.S. families. Liquidity constrained families are estimated to constitute 19.4 percent of the population sampled, a group that accounts for 16.7 percent of consumption in the population sampled. In-sample simulations of the model suggest that a temporary tax has three to four times more impact on aggregate consumption than it would if liquidity constraints were not in effect. Copyright 1987 by The Econometric Society.

The authors investigate the effect of opening a forward or futures market on spot price or real exchange rate variab ility in a two-agent, two-good, two-state, general-equilibrium model. This is shown to depend upon such familiar parameters as substitutio n elasticities, marginal propensities to consume, and degress of risk aversion. The analysis highlights the importance of the income trans fer, which occurs as a result of capital gains and losses in the forw ard market. The authors find some presumption in favor of the view th at opening a forward market reduces spot price variability. The presu mption is strengthened the less risk averse are agents. Copyright 1987 by The Econometric Society.

This paper examines a market with asymmetric information where there are many signals available and where both the costs of signaling and the product value may depend on many privately known characteristics. Under a weak condition on the relationship between the marginal cost of increasing the signals and the product value, a separating set exists whereby the value of every seller's product is inferred from the seller's optimal choice of signals. The separating set constructed is Pareto dominant and corresponds to recently proposed equilibrium notions in signaling and screening models. Copyright 1987 by The Econometric Society.

A generalization of the multinomial logit (MNL) model is developed for cases in which discrete alternatives are ordered so as to induce stochastic correlation among alternatives in close proximity. The model belongs to the Generalized Extreme Value class introduced by McFadden, and is therefore consistent with random utility maximization. If the true model is nearly MNL, iterative estimation on an ordinary MNL computer package provides approximate parameter estimates and a test for the hypothesized failure of the MNL'S "independence from irrelevant alternatives" assumption. A straightforward extension can handle cases where observations have been selected on the basis of a truncated choice set. The model's properties are investigated through a numerical example, and through two empirical applications whose rather unsatisfactory results are very briefly described.

This paper studies the sequential equilibria of signaling games. It introduces a new solution concept, divine equilibrium, that refines the set of sequential equilibria by requiring that off-the-equilibrium-path beliefs satisfy an additional restriction. This restriction rules out implausible sequential equilibria in many examples. We show that divine equilibria exist by demonstrating that a sequential equilibrium that fails to be divine cannot be in a stable component. However, the stable component of signaling games is typically smaller than the set of divine equilibria. We demonstrate this fact through examples. We also present a characterization of the stable equilibria in generic signaling games.

The author proposes a refinement of seq uential equilibrium for extensive form games by generalizing a restri ction proposed for signaling games in Cho and D. M. Kreps (1987). The restriction is that beliefs must not assign positive weight to the p ossibilities that can be excluded through reasonable introspection ba sed on the data available as common knowledge. A new technique is dev eloped in order to prove the existence of forward induction equilibri um, which consists of two steps. First, the author establishes the ge neric existence of forward induction equilibrium by exploiting the re sults of E. Kohlberg and J. F. Mertens (1986). Then, he shows that th e forward induction equilibrium correspondence is upper hemicontinuou s in the outcome space with respect to the changes of parameters of t he game. Copyright 1987 by The Econometric Society.

The paper deals with infinite horizon optimization problems. The existence of optimal solutions is obtained as a consequence of an asymptotic growth condition. We also exhibit finite horizon approximates that yield upper and lower bounds for the optimal values and whose optimal solutions converge to the long-term optimal trajectories.

This paper provides two results that are useful in proving the exist ence of and characterizing separating equilibria in signaling games. A key element in the analysis of separating equilibria is the examina tion of the implied incentive compatibility constraints. It is shown that these constraints imply differentiability of strategies. In addi tion, a monotonicity condition (which is similar to the single crossi ng condition) is analyzed that is necessary and sufficient for there to be a strategy satisfying the incentive compatibility constraints. As a direct consequence of these two results, the analysis of Paul Milgrom and John Roberts (1982) is considerably strengthened. Copyright 1987 by The Econometric Society.