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201901Screening and Adverse Selection in Frictional Markets.pdf
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201901Screening and Adverse Selection in Frictional Markets.pdf
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Screening and Adverse Selection in Frictional
Markets
∗
Benjamin Lester
Federal Reserve Bank of Philadelphia
Ali Shourideh
Carnegie Mellon University
Venky Venkateswaran
NYU – Stern School of Business
Ariel Zetlin-Jones
Carnegie Mellon University
September 19, 2018
∗
We thank Gadi Barlevy, Hanming Fang, Mike Golosov, Piero Gottardi, Veronica Guerrieri, Ali Hor-
tacsu, Alessandro Lizzeri, Guido Menzio, Derek Stacey, Robert Townsend, Randy Wright, and Pierre
Yared, along with seminar participants at the Spring 2015 Search and Matching Workshop, 2015 CIGS Con-
ference on Macroeconomic Theory and Policy, 2015 annual meeting of the Society for Economic Dynamics,
2015 meeting of the Society for the Advancement of Economic Theory, 2015 Norges Bank Conference on
Financial Stability, 4th Rome Junior Conference on Macroeconomics (EIEF), 2015 Summer Workshop on
Money, Banking, Payments and Finance at the Federal Reserve Bank of St. Louis, 2015 West Coast Search
and Matching, 2015 Vienna Macro Workshop, NYU Search Theory Workshop, European University Insti-
tute, Toulouse School of Economics, University of Pennsylvania, Columbia University, the Federal Reserve
Bank of Cleveland, and the Banque de France for useful discussions and comments. The views expressed
here are those of the authors and do not necessarily reflect the views of the Federal Reserve Bank of
Philadelphia or the Federal Reserve System.
1
Manuscript (tex file) Click here to
access/download;Manuscript;LSVZ_revision2_final.tex
Copyright The University of Chicago 2018. Preprint (not copyedited or formatted).
Please use DOI when citing or quoting. DOI: 10.1086/700729
This content downloaded from 185.216.093.030 on September 29, 2018 14:07:37 PM
All use subject to University of Chicago Press Terms and Conditions (http://www.journals.uchicago.edu/t-and-c).
Abstract
We incorporate a search-theoretic model of imperfect competition into a standard
model of asymmetric information with unrestricted contracts. We characterize the
unique equilibrium, and use our characterization to explore the interaction between
adverse selection, screening, and imperfect competition. We show that the relation-
ship between an agent’s type, the quantity he trades, and the price he pays is jointly
determined by the severity of adverse selection and the concentration of market
power. Therefore, quantifying the effects of adverse selection requires controlling
for market structure. We also show that increasing competition and reducing infor-
mational asymmetries can decrease welfare.
Keywords: Adverse Selection, Imperfect Competition, Screening, Transparency, Search
Theory
JEL Codes: D41, D42, D43, D82, D83, D86, L13
2
Copyright The University of Chicago 2018. Preprint (not copyedited or formatted).
Please use DOI when citing or quoting. DOI: 10.1086/700729
This content downloaded from 185.216.093.030 on September 29, 2018 14:07:37 PM
All use subject to University of Chicago Press Terms and Conditions (http://www.journals.uchicago.edu/t-and-c).
1 Introduction
Many important markets suffer from adverse selection, including the markets for insur-
ance, credit, and certain financial securities. There is mounting evidence that many of
these markets also feature some degree of imperfect competition.
1
And yet, perhaps
surprisingly, the effect of imperfect competition on prices, allocations, and welfare in
markets with adverse selection remains an open question.
Answering this question is important for several reasons. For one, many empirical
studies attempt to quantify the effects of adverse selection in the markets mentioned
above.
2
A natural question is to what extent these estimates—and the conclusions that
follow—are sensitive to the assumptions imposed on the market structure. There has
also been a recent push by policymakers to make these markets more competitive and
less opaque.
3
Again, a crucial, but underexplored question is whether these attempts
to promote competition and reduce information asymmetries are necessarily welfare-
improving.
Unfortunately, the ability to answer these questions has been constrained by a short-
age of appropriate theoretical frameworks.
4
A key challenge is to incorporate nonlinear
pricing schedules—which are routinely used to screen different types of agents—into
a model with asymmetric information and imperfect competition. This paper delivers
such a model: we develop a novel, tractable framework of adverse selection, screening,
and imperfect competition.
The key innovation is to introduce a search-theoretic model of imperfect competition
1
For evidence of market power in insurance markets, see Brown and Goolsbee (2002), Dafny (2010),
and Cabral et al. (2014). For evidence of market power in various credit markets, see, e.g., Ausubel (1991),
Calem and Mester (1995), and Crawford et al. (2015). In over-the-counter financial markets, a variety
of data suggest that dealers extract significant rents; indeed, this finding is hard-wired into workhorse
models of this market, such as Duffie et al. (2005).
2
See the seminal paper by Chiappori and Salanie (2000), and Einav et al. (2010a) for a comprehensive
survey.
3
Increasing competition and transparency in health insurance markets is a cornerstone of the Afford-
able Care Act, while the Dodd-Frank legislation addresses similar issues in over-the-counter financial
markets. In credit markets, on the other hand, legislation has recently focused on restricting how much
information lenders can demand or use from borrowers.
4
As Chiappori et al. (2006) put it, “there is a crying need for [a model] devoted to the interaction
between imperfect competition and adverse selection.”
3
Copyright The University of Chicago 2018. Preprint (not copyedited or formatted).
Please use DOI when citing or quoting. DOI: 10.1086/700729
This content downloaded from 185.216.093.030 on September 29, 2018 14:07:37 PM
All use subject to University of Chicago Press Terms and Conditions (http://www.journals.uchicago.edu/t-and-c).
(a la Burdett and Judd, 1983) into an otherwise standard model with asymmetric infor-
mation and nonlinear contracts. Within this environment, we provide a full analytical
characterization of the unique equilibrium, and then use this characterization to study
both the positive and normative issues highlighted above.
First, we show how the structure of equilibrium contracts—and hence the relation-
ship between an agent’s type, the quantity that he trades, and the corresponding price—
is jointly determined by the severity of the adverse selection problem and the degree of
imperfect competition. In particular, we show that equilibrium offers separate different
types of agents when competition is relatively intense or adverse selection is relatively se-
vere, while they typically pool different types of agents in markets where principals have
sufficient market power and adverse selection is sufficiently mild. Second, we explore
how total trading volume—which, in our environment, corresponds to the utilitarian
welfare measure—responds to changes in the degree of competition and the severity of
adverse selection. We show that increasing competition or reducing informational asym-
metries is only welfare-improving in markets in which both market power is sufficiently
concentrated and adverse selection is sufficiently severe.
Before expanding on these results, it is helpful to lay out the basic ingredients of the
model. The agents, whom we call “sellers,” are endowed with a perfectly divisible good
of either low or high quality, which is private information. The principals, whom we
call “buyers,” offer menus containing price-quantity combinations to potentially screen
high- and low-quality sellers.
5
Sellers can accept at most one contract, i.e., contracts are
exclusive. To this otherwise canonical model of trade under asymmetric information, we
introduce imperfect competition by endowing the buyers with some degree of market
power. The crucial assumption is that each seller receives a stochastic number of offers,
with a positive probability of receiving only one. Hence, when a buyer formulates
an offer, he understands that it will be compared with an alternative offer with some
probability, which we denote by π, and it will be the seller’s only option with probability
5
The use of the labels “buyers” and “sellers” is merely for concreteness and corresponds most clearly
with an asset market interpretation. These monikers can simply be switched in the context of an insurance
market, so that the “buyers” of insurance are the agents with private information and the “sellers” of
insurance are the principals.
4
Copyright The University of Chicago 2018. Preprint (not copyedited or formatted).
Please use DOI when citing or quoting. DOI: 10.1086/700729
This content downloaded from 185.216.093.030 on September 29, 2018 14:07:37 PM
All use subject to University of Chicago Press Terms and Conditions (http://www.journals.uchicago.edu/t-and-c).
1 − π. This formulation allows us to capture the perfectly competitive case by setting
π = 1, the monopsony case by setting π = 0, and everything in between.
For the general case of imperfect competition, with π ∈ (0, 1), the equilibrium in-
volves buyers mixing over menus according to a nondegenerate distribution function.
6
Since each menu is comprised of two price-quantity pairs (one for each type), the main
equilibrium object is a probability distribution over four-dimensional offers. An impor-
tant contribution of our paper is developing a methodology that allows for a complete,
yet tractable, characterization of this complicated equilibrium object.
We begin by showing that any menu can be summarized by the indirect utilities it of-
fers to sellers of each type. Next, we establish an important property: in any equilibrium,
all menus that are offered by buyers are ranked in exactly the same way by both low-
and high-quality sellers. This property, which we call “strictly rank-preserving,” implies
that all equilibrium menus can be ranked along a single dimension. The equilibrium,
then, can be described by a distribution function over a unidimensional variable—say,
the indirect utility offered to low-quality sellers—along with a strictly monotonic func-
tion mapping this variable to the indirect utility offered to the high-quality seller. We
show how to solve for these two functions, obtaining a full analytical characterization
of all equilibrium objects of interest, and then establish that the equilibrium is unique.
Interestingly, our approach not only avoids the well-known problems with existence of
equilibria in models of adverse selection and screening, but also requires no assumptions
on off-path beliefs to get uniqueness. We then use this characterization to explore the
implications of imperfect competition in markets suffering from adverse selection.
First, we show that the structure of menus offered in equilibrium depends on both the
degree of competition, captured by π, and the severity of the adverse selection problem,
which is succinctly summarized by a single statistic that is largest (i.e., adverse selection
is most severe) when: (i) the fraction of low-quality sellers is large; (ii) the potential
6
Mixing is to be expected for at least two reasons. First, this is a robust feature of nearly all models
in which buyers are both monopsonists and Bertrand competitors with some probability, even without
adverse selection or nonlinear contracts. Second, even in perfectly competitive markets, it is well known
that pure strategy equilibria may not exist in an environment with both adverse selection and nonlinear
contracts.
5
Copyright The University of Chicago 2018. Preprint (not copyedited or formatted).
Please use DOI when citing or quoting. DOI: 10.1086/700729
This content downloaded from 185.216.093.030 on September 29, 2018 14:07:37 PM
All use subject to University of Chicago Press Terms and Conditions (http://www.journals.uchicago.edu/t-and-c).
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