The current literature on mechanism design in models with social preferences discusses social-preference-robust mechanisms, i.e., mechanisms that are implementable in any environment with social preferences. The literature also discusses payoff-information-robust mechanisms, i.e., mechanisms that are implementable for any belief and higher-order beliefs of the agents about the payoff types of the other agents. In the present paper, I address the question of whether deterministic mechanisms that are robust in both of these dimensions exist. I consider environments where each agent holds private information about his personal payoff and about the existence and extent of his social preferences. In such environments, a mechanism is robust in both dimensions only if it is ex-post implementable, i.e., only if incentive compatibility holds for every realization of payoff signals and for every realization of social preferences. I show that ex-post implementation of deterministic mechanisms is impossible in such environments; i.e., deterministic mechanisms that are both social-preference-robust and payoff-information-robust do not exist.

A seller of an item faces a potential buyer whose valuation of the item depends on two private signals. It is well known that when there are informational externalities and the buyer’s private signals arrive all at once, it is impossible to implement an efficient sale. I show that if the buyer’s private signals arrive over time, then the seller can implement an efficient sale even in the presence of informational externalities. Specifically, I present a novel condition on the relationship between the buyer’s valuation and the social welfare that is necessary and sufficient for efficient sequential implementation.

We study a receiver's learning problem of choosing an informative test in a signaling environment. Each test induces a signaling subgame. Thus, in addition to its direct effect on the receiver's information, a test has an indirect effect through the sender's signaling strategy. We show that the informativeness of signaling in the equilibrium that a test induces depends on the relative informativeness of the test's high and low grades. Consequently, we find that the receiver's preference relation over tests needs not comply with Blackwell's (1951) order. Our findings may shed light on phenomena such as grade inflation and information coarsening.

We study the implications of the disclosure regime of ratings on the level of information released to the public. Specifically, we compare mandatory and voluntary disclosure. We analyze a model where the potential issuers are initially endowed with homogeneous soft information about their values before paying to acquire ratings. We find that for every accuracy level of the issuers’ initial information, voluntary disclosure results in a more informative equilibrium than mandatory disclosure. This finding identifies a dimension in which the existing European Union regulations that impose the mandatory disclosure of ratings may lead to a loss of information to the public. (JEL D21, D42, D43, D82, D83, G24)