Scott Duke Kominers

Stability and competitive equilibrium in trading networks

We introduce a model in which agents in a network can trade via bilateral contracts. We find that when continuous transfers are allowed and utilities are quasi-linear, the full substitutability of preferences is sufficient to guarantee the existence of stable outcomes for any underlying network structure. Furthermore, the set of stable outcomes is essentially equivalent to the set of competitive equilibria, and all stable outcomes are in the core and are efficient. By contrast, for any domain of preferences strictly larger than that of full substitutability, the existence of stable outcomes and competitive equilibria cannot be guaranteed.

Contract design and stability in many-to-many matching

We develop a model of many-to-many matching with contracts that subsumes as special cases many-to-many matching markets and buyer–seller markets with heterogeneous and indivisible goods. In our setting, substitutable preferences are sufficient to guarantee the existence of stable outcomes; moreover, in contrast to results for the setting of many-to-one matching with contracts, if any agents preferences are not substitutable, then the existence of a stable outcome can not be guaranteed.

Design and implementation of a privacy preserving electronic health record linkage tool in Chicago

OBJECTIVE To design and implement a tool that creates a secure, privacy preserving linkage of electronic health record (EHR) data across multiple sites in a large metropolitan area in the United States (Chicago, IL), for use in clinical research. METHODS The authors developed and distributed a software application that performs standardized data cleaning, preprocessing, and hashing of patient identifiers to remove all protected health information. The application creates seeded hash code combinations of patient identifiers using a Health Insurance Portability and Accountability Act compliant SHA-512 algorithm that minimizes re-identification risk. The authors subsequently linked individual records using a central honest broker with an algorithm that assigns weights to hash combinations in order to generate high specificity matches. RESULTS The software application successfully linked and de-duplicated 7 million records across 6 institutions, resulting in a cohort of 5 million unique records. Using a manually reconciled set of 11 292 patients as a gold standard, the software achieved a sensitivity of 96% and a specificity of 100%, with a majority of the missed matches accounted for by patients with both a missing social security number and last name change. Using 3 disease examples, it is demonstrated that the software can reduce duplication of patient records across sites by as much as 28%. CONCLUSIONS Software that standardizes the assignment of a unique seeded hash identifier merged through an agreed upon third-party honest broker can enable large-scale secure linkage of EHR data for epidemiologic and public health research. The software algorithm can improve future epidemiologic research by providing more comprehensive data given that patients may make use of multiple healthcare systems.

On the correspondence of contracts to salaries in (many-to-many) matching

In this note, I extend the work of Echenique (2012) to show that a model of many-to-many matching with contracts may be embedded into a model of many-to-many matching with wage bargaining whenever (1) all agentsʼ preferences are substitutable and (2) the matching with contracts model is unitary, in the sense that every contractual relationship between a given firm–worker pair is specified in a single contract. Conversely, I show that unitarity is essentially necessary for the embedding result.

Computer vision uncovers predictors of physical urban change

Significance We develop a computer vision method to measure changes in the physical appearances of neighborhoods from street-level imagery. We correlate the measured changes with neighborhood characteristics to determine which characteristics predict neighborhood improvement. We find that both education and population density predict improvements in neighborhood infrastructure, in support of theories of human capital agglomeration. Neighborhoods with better initial appearances experience more substantial upgrading, as predicted by the tipping theory of urban change. Finally, we observe more improvement in neighborhoods closer to both city centers and other physically attractive neighborhoods, in agreement with the invasion theory of urban sociology. Our results show how computer vision techniques, in combination with traditional methods, can be used to explore the dynamics of urban change. Which neighborhoods experience physical improvements? In this paper, we introduce a computer vision method to measure changes in the physical appearances of neighborhoods from time-series street-level imagery. We connect changes in the physical appearance of five US cities with economic and demographic data and find three factors that predict neighborhood improvement. First, neighborhoods that are densely populated by college-educated adults are more likely to experience physical improvements—an observation that is compatible with the economic literature linking human capital and local success. Second, neighborhoods with better initial appearances experience, on average, larger positive improvements—an observation that is consistent with “tipping” theories of urban change. Third, neighborhood improvement correlates positively with physical proximity to the central business district and to other physically attractive neighborhoods—an observation that is consistent with the “invasion” theories of urban sociology. Together, our results provide support for three classical theories of urban change and illustrate the value of using computer vision methods and street-level imagery to understand the physical dynamics of cities.

Hinged Dissections Exist

We prove that any finite collection of polygons of equal area has a common hinged dissection. That is, for any such collection of polygons there exists a chain of polygons hinged at vertices that can be folded in the plane continuously without self-intersection to form any polygon in the collection. This result settles the open problem about the existence of hinged dissections between pairs of polygons that goes back implicitly to 1864 and has been studied extensively in the past ten years. Our result generalizes and indeed builds upon the result from 1814 that polygons have common dissections (without hinges). Our proofs are constructive, giving explicit algorithms in all cases. For two planar polygons whose vertices lie on a rational grid, both the number of pieces and the running time required by our construction are pseudopolynomial. This bound is the best possible, even for unhinged dissections. Hinged dissections have possible applications to reconfigurable robotics, programmable matter, and nanomanufacturing.

Multilateral matching

We introduce a matching model in which agents engage in joint ventures via multilateral contracts. This approach allows us to consider production complementarities previously outside the scope of matching theory. We show analogues of the rst and second welfare theorems, and, when agents’ utilities are concave in venture participation, show that competitive equilibria exist, correspond to stable outcomes, and yield core outcomes. Competitive equilibria exist in our setting even when externalities are present. JEL classication: C78; C62; C71; D47; D85; L14; L24

Patent Trolls: Evidence from Targeted Firms

We develop a theoretical model of, and provide the first large-sample evidence on, the behavior and impact of non-practicing entities (NPEs) in the intellectual property space. Our model shows that NPE litigation can reduce infringement and support small inventors. However, the model also shows that as NPEs become effective at bringing frivolous lawsuits, the resulting defense costs inefficiently crowd out firms that, absent NPEs, would produce welfare-enhancing innovations without engaging in infringement. Our empirical analysis shows that on average, NPEs behave as opportunistic patent trolls. NPEs sue cash-rich firms ― a one standard deviation increase in cash holdings roughly doubles a firms chance of being targeted by NPE litigation. We find moreover that NPEs target cash unrelated to the alleged infringement at essentially the same frequency as they target cash related to the alleged infringement. By contrast, cash is neither a key driver of intellectual property lawsuits by practicing entities (e.g., IBM and Intel), nor of any other type of litigation against firms. We find further suggestive evidence of NPE opportunism, such as forum shopping and targeting of firms that have reduced ability to defend themselves against litigation. We find that NPE litigation has a real negative impact on innovation at targeted firms: firms substantially reduce their innovative activity after settling with NPEs (or losing to them in court). Moreover, we neither find any markers of significant NPE pass-through to end innovators, nor of a positive impact of NPEs on innovation in the industries in which they are most prevalent.

The growing problem of patent trolling

Cash-hungry patent trolls are squelching innovation—and should be screened out The last decade has seen a sharp rise in patent litigation in the United States; 2015 has one of the highest patent lawsuit counts on record (1). In theory, this could reflect growth in commercialization of technology and innovation—lawsuits increase as more firms turn to intellectual property (IP) protection to safeguard their competitive advantages. However, the majority of recent patent litigation is driven by nonpracticing entities (NPEs), firms that generate no products but amass patent portfolios for the sake of “enforcing” IP rights (2). We discuss new, large-sample evidence adding to a growing literature (3–7) that suggests that NPEs—in particular, large patent aggregators—on average, act as “patent trolls,” suing cash-rich firms seemingly irrespective of actual patent infringement. This has a negative impact on innovation activity at targeted firms. These results suggest a need to change U.S. IP policy, particularly to screen out trolling early in the litigation process.

Concordance Among Holdouts

Holdout problems prevent decentralized aggregation of complementary goods, but the coercion required to overcome holdout may encourage abuse and violate fairness standards. We propose second-best efficiency, abuse-prevention, and fairness criteria for procedures intended to reduce holdout. Our criteria are jointly satisfied by a class of “Concordance” procedures. In these procedures, the prospective buyer makes a take-it-or-leave-it offer to the group of sellers, and the sellers use an efficient collective choice mechanism to decide as a group whether to accept the buyer’s offer. In the case of sale, the buyer’s offer is divided among the sellers in a fashion independent of individual sellers’ actions. Each seller retains the option to receive, in the event of sale, her share of the offer (without making any additional payments) in exchange for not influencing the collective decision. Our approach is applicable in a range of contexts including land assembly, spectrum aggregation, corporate acquisitions, and patent pool formation.