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A seller designs a mechanism to sell a single object to a potential buyer whose private type is his incomplete information about his valuation. The seller can disclose additional information to the buyer about his valuation without observing its realization. In both discrete-type and continuous-type settings, we show that discriminatory disclosure—releasing different amounts of additional information to different buyer types—dominates full disclosure in terms of seller revenue. An implication is that the orthogonal decomposition technique, while an important tool in dynamic mechanism design, is generally invalid when information disclosure is part of the design.

Mediation by sulphate-reducing bacteria (SRB) is responsible for pyrite (FeS 2 ) formation. The origin of the Dachang tin polymetallic ore field is related to the mineralisation of submarine hydrothermal vent sediments. Here, we investigated SRB in these ores via morphological, chemical, and isotopic analyses. Polarised and scanning electron microscopy indicated that trace SRB fossils in the metal sulphide ore were present in the form of tubular, beaded, and coccoidal bodies comprising FeS 2 and were enclosed within a pyrrhotite (FeS) matrix in the vicinity of micro-hydrothermal vents. The carbon (C), nitrogen (N), and oxygen (O) contents in the FeS 2 synthesised by SRB were high, and a clear biological Raman signal was detected. No such signals were discerned in the peripheral FeS. This co-occurrence of FeS, FeS 2 , and the remains of bacteria (probably chemoautotrophic bacteria) was interpreted as the coprecipitation process of SRB-mediated FeS 2 formation, which has, to the best of our knowledge, not been reported before. Our study also illustrates that combined energy-dispersive X-ray spectroscopy, Raman spectroscopy, and isotopic analysis can be used as a novel methodology to document microbial-mediated processes of mineral deposition in submarine hydrothermal vent ecology on geological time scales.

We derive the incentive compatible and ex-ante welfare maximizing (i.e. utilitarian) mechanism for settings with an arbitrary number of agents and alternatives where the privately informed agents have single-crossing and single-peaked preferences. The optimal outcome can be implemented by modifying a sequential voting scheme that is used in many legislatures and committees. The modification uses a flexible majority threshold for each of several alternatives, and allows us to replicate, via a single sequential procedure, the entire class of anonymous, unanimous, and dominant strategy incentive compatible mechanisms. Our analysis relies on elegant characterizations of this class of mechanisms for single-peaked and single-crossing preferences.

We study the role of limited commitment in a standard auction environment. In each period, the seller can commit to an auction with a reserve price but not to future reserve prices. We characterize the set of equilibrium profits attainable for the seller as the period length vanishes. An immediate sale by efficient auction is optimal when there are at least three buyers. For many natural distributions two buyers is enough. Otherwise, we give conditions under which the maximal profit is attained through continuously declining reserve prices.

We study the optimal design of organizations under the assumption that agents in a contest care about their relative position. A principal determines the number and size of status categories in order to maximize output. We first consider the pure status case without tangible prizes. Our results connect the optimal partition in status categories to properties of the distribution of ability among contestants. The top status category always contains a unique element. For distributions that have an increasing failure rate (IFR), a proliferation of status classes is optimal, whereas the optimal partition involves only two categories if the distribution of abilities is sufficiently concave. Moreover, for IFR distributions, a coarse partition with two status categories achieves at least half of the output obtained in the optimal partition with many categories. Finally, if status is derived solely from monetary rewards, we show that the optimal partition in status classes contains only two categories.

A committee decides by unanimity whether to accept the current alternative, or to continue costly search. Each alternative is described by a vector of distinct attributes, and each committee member can privately assess the quality of one attribute (her \"specialty\"). Preferences are heterogeneous and interdependent: each specialist values all attributes, but puts a higher weight on her specialty (partisanship). We study how acceptance standards and members' welfare vary with the amount of conflict within the committee. We also compare decisions made by committees consisting of specialized experts to decisions made by committees of generalists who can each assess all information available. The acceptance standard decreases (increases) in the degree of conflict when information is public (private). In both cases welfare decreases in the level of conflict. Finally, we identify situations where specialized committee decisions yield Pareto improvements over specialized, one-person decisions and over committee decisions made by generalists.

We consider a standard social choice environment with linear utilities and independent, one-dimensional, private types. We prove that for any Bayesian incentive compatible mechanism there exists an equivalent dominant strategy incentive compatible mechanism that delivers the same interim expected utilities for all agents and the same ex ante expected social surplus. The short proof is based on an extension of an elegant result due to Gutmann, Kemperman, Reeds, and Shepp (1991). We also show that the equivalence between Bayesian and dominant strategy implementation generally breaks down when the main assumptions underlying the social choice model are relaxed or when the equivalence concept is strengthened to apply to interim expected allocations.

We study a multi-dimensional collective decision under incomplete information. Agents have Euclidean preferences and vote by simple majority on each issue (dimension), yielding the coordinate-wise median. Judicious rotations of the orthogonal axes -- the issues that are voted upon -- lead to welfare improvements. If the agents' types are drawn from a distribution with independent marginals then, under weak conditions, voting on the original issues is not optimal. If the marginals are identical (but not necessarily independent), then voting first on the total sum and next on the differences is often welfare superior to voting on the original issues. We also provide various lower bounds on incentive efficiency: in particular, if agents' types are drawn from a log-concave density with I.I.D. marginals, a second-best voting mechanism attains at least 88% of the first-best efficiency. Finally, we generalize our method and some of our insights to preferences derived from distance functions based on inner products.

In frictional matching markets with heterogeneous buyers and sellers, sellers incur discrete showing costs to show goods to buyers who incur discrete inspection costs to assess the suitability of the goods on offer. We study how brokers can help reduce these costs by managing the level and mix of goods in their inventory. Intermediaries emerge and improve social welfare when there is sufficient heterogeneity in the types of goods and preferences. Learning and inventory management enable search intermediaries to internalize information externalities generated in unintermediated private search. Externalités informationnelles et intermédiaires dans des marchés frictionnels de recherche. Dans des marchés frictionnels d'arrimage où acheteurs et vendeurs sont hétérogènes, les vendeurs doivent encourir des coûts séparés pour montrer leurs produits aux acheteurs qui doivent pour leur part encourir des coûts séparés d'inspection pour s'assurer que les biens offerts leur conviennent. On étudie comment des courtiers peuvent aider à réduire ces coûts en gérant le niveau et la mixité des biens dans leurs inventaires. Des intermédiaires émergent qui améliorent le bien-être social quand il y a hétérogénéité suffisante des types de biens et de préférences. L'apprentissage et la gestion des inventaires permettent aux intermédiaires de recherche d'internaliser les externalités informationnelles engendrées dans le processus de recherche privée sans l'aide d'intermédiaires.