Matthew Shum

Do Mergers Improve Information? Evidence from the Loan Market

We examine the informational effects of M&As by investigating whether bank mergers improve banks’ ability to screen borrowers. By exploiting a dataset in which we observe a measure of a borrower’s default risk that the lenders observe only imperfectly, we find evidence of these informational improvements. Mergers lead to a closer correspondence between interest rates and individual default risk: after a merger, risky borrowers experience an increase in the interest rate, while non-risky borrowers enjoy lower interest rates. These informational benefits appear to derive from improvements in information processing resulting from the merger, rather than from explicit information sharing on individual customers among the merging parties. Our evidence suggests that part of these informational improvements stem from the consolidated banks using ‘hard’ information more intensively.

The Money Pump as a Measure of Revealed Preference Violations

We introduce a measure of the severity of violations of the revealed preference axioms, the money pump index (MPI). The MPI is the amount of money one can extract from a consumer who violates the axioms. It is also a statistical test for the hypothesis that a consumer is rational when behavior is observed with error. We present an application using a panel data set of food expenditures. The data exhibit many violations of the axioms. Mostly, the MPI for these violations is small. The MPI indicates that the hypothesis of consumer rationality cannot be rejected.

Econometric models of asymmetric ascending auctions

We develop econometric models of ascending (English) auctions which allow for both bidder asymmetries as well as common and/or private value components in bidders’ underlying valuations. We show that the equilibrium inverse bid functions in each round of the auction are implicitly defined (pointwise) by a system of nonlinear equations, so that conditions for the existence and uniqueness of an increasing-strategy equilibrium are essentially identical to those which ensure a unique and increasing solution to the system of equations. We exploit the computational tractability of this characterization in order to develop an econometric model, thus extending the literature on structural estimation of auction models. Finally, an empirical example illustrates how equilibrium learning affects bidding during the course of the auction.

Monopoly Quality Degradation and Regulation in Cable Television

Using an empirical framework based on the Mussa‐Rosen model of monopoly quality choice, we calculate the degree of quality degradation in cable television markets and the impact of regulation on those choices. We find lower bounds of quality degradation ranging from 11 to 45 percent of offered service qualities. Furthermore, cable operators in markets with local regulatory oversight offer significantly higher quality, less degradation, and greater quality per dollar, despite higher prices.

Generalized Empirical Likelihood Based Model Selection Criteria For Moment Condition Models

This paper proposes model selection criteria (MSC) for unconditional moment models using generalized empirical likelihood (GEL) statistics. The use of GEL-statistics in lieu of J-statistics (in the spirit of Andrews, 1999, Econometrica 67, 543-564; and Andrews and Lu, 2001, Journal of Econometrics 101, 123-164) leads to an alternative interpretation of the MSCs that emphasizes the common information-theoretic rationale underlying model selection procedures for both parametric and semiparametric models. The result of this paper also provides a GEL-based model selection alternative to the information criteria-based nonnested tests for generalized method of moments models considered in Kitamura (2000, University of Wisconsin). The results of a Monte Carlo experiment are reported to illustrate the finite-sample performance of the selection criteria and their impact on parameter estimation.

Nonlinear Pricing with Self-Control Preferences

A basic assumption of economics is that consumers choose what they want. However, many consumers find it difficult to stop overeating, overspending, smoking, procrastinating, etc, even though they want to. In reality, consumers have temptation and it is psychologically costly to exercise self-control. To clarify the implications of the existence of temptation and self-control costs, this paper studies a firm’s optimal selling strategy exploiting the behavioral features of consumers. We characterize optimal nonlinear pricing schemes for a monopoly when self-control is costly for consumers. Since consumers have a preference for commitment, the firm faces a trade-off between offering a small menu that makes the consumers’ self-control easier and offering a large menu that achieves better price discrimination. We show that the optimal menu resembles the one in the standard nonlinear pricing problem with a price ceiling, where the upper bound on prices is determined endogenously by a participation constraint. The ceiling motivates the firm to offer a relatively flat and compact price schedule, serving more consumers with low demand. The characterization also shows that the firm may earn less if consumers have temptation.

Rates of information aggregation in common value auctions

We study the rates at which transaction prices aggregate information in common value auctions under the different information structures in Wilson (Rev. Econ. Stud. 44 (1977) 511) and Pesendorfer and Swinkels (Econometrica 65 (1997) 1247). We consider uniform-price auctions in which k identical objects of unknown value are auctioned to n bidders, where both n and k are allowed to diverge to infinity, and k/n converges to a number in [0,1). The Wilson assumptions lead to information aggregation at a rate proportional to n/√k , but the price aggregates information at a rate proportional to n/√k in the PS setting. We also consider English auctions, and investigate whether the extra information revealed in equilibrium improves convergence rates in these auctions.

Superstition and “lucky” apartments: Evidence from transaction-level data

Using a sample of apartment transactions during 2004-2006 in Chengdu, China, we investigate the impact of superstitions in the Chinese real estate market. Numerology forms an important component of Chinese superstitious lore, with the numbers 8 and 6 signifying good luck, and the number 4 bad luck. We find that secondhand apartments located on floors ending with “8�? fetch, on average, a 235 RMB higher price (per square meter) than on other floors. For newly constructed apartments, this price premium disappears due to uniform pricing of new housing units, but apartments on floors ending in an “8�? are sold, on average, 6.9 days faster than on other floors. Buyers who have a phone number containing more “8�?’s are more likely to purchase apartments in a floor ending with “8�?; this suggests that at least part of the price premium for “lucky�? apartments arises from the buyers’ superstitious beliefs.

Duality in dynamic discrete‐choice models

Using results from Convex Analysis, we investigate a novel approach to identification and estimation of discrete‐choice models that we call the mass transport approach. We show that the conditional choice probabilities and the choice‐specific payoffs in these models are related in the sense of conjugate duality, and that the identification problem is a mass transport problem. Based on this, we propose a new two‐step estimator for these models; interestingly, the first step of our estimator involves solving a linear program that is identical to the classic assignment (two‐sided matching) game of Shapley and Shubik (1971). The application of convex‐analytic tools to dynamic discrete‐choice models and the connection with two‐sided matching models is new in the literature. Monte Carlo results demonstrate the good performance of this estimator, and we provide an empirical application based on Rusts (1987) bus engine replacement model.

Aggregate matchings

This paper characterizes the testable implications of stability for aggregate matchings. We consider data on matchings where individuals are aggregated, based on their observable characteristics, into types, and we know how many agents of each type match. We derive stability conditions for an aggregate matching, and, based on these, provide a simple necessary and sufficient condition for an observed aggregate matching to be rationalizable (i.e. such that preferences can be found so that the observed aggregate matching is stable). Subsequently, we derive moment inequalities based on the stability conditions, and provide an empirical illustration using the cross-sectional marriage distributions across the US states.