Jungyoll Yun

Department of Economics,
Ewha University,

Institutional Affiliation: Ewha University, Seoul, Korea

NBER Working Papers and Publications

June 2018Characterization, Existence, and Pareto Optimality in Insurance Markets with Asymmetric Information with Endogenous and Asymmetric Disclosures: Revisiting Rothschild-Stiglitz
with Joseph E. Stiglitz, Andrew Kosenko: w24711
We study the Rothschild-Stiglitz model of competitive insurance markets with endogenous information disclosure by both firms and consumers. We show that an equilibrium always exists, (even without the single crossing property), and characterize the unique equilibrium allocation. With two types of consumers the outcome is particularly simple, consisting of a pooling allocation which maximizes the well-being of the low risk individual (along the zero profit pooling line) plus a supplemental (undisclosed and nonexclusive) contract that brings the high risk individual to full insurance (at his own odds). We show that this outcome is extremely robust and Pareto efficient.
June 2017Equilibrium in a Competitive Insurance Market Under Adverse Selection with Endogenous Information
with Joseph E. Stiglitz, Andrew Kosenko: w23556
This paper investigates the existence and nature of equilibrium in a competitive insurance market under adverse selection with endogenously determined information structures. Rothschild-Stiglitz (RS) characterized the self-selection equilibrium under the assumption of exclusivity, enforcement of which required full information about contracts purchased. By contrast, the Akerlof price equilibrium described a situation where the insurance firm has no information about sales to a particular individual. We show that with more plausible information assumptions - no insurance firm has full information but at least knows how much he has sold to any particular individual - neither the RS quantity constrained equilibrium nor the Akerlof price equilibrium are sustainable. But when the informat...
August 2013Optimality and Equilibrium In a Competitive Insurance Market Under Adverse Selection and Moral Hazard
with Joseph Stiglitz: w19317
This paper analyzes optimal and equilibrium insurance contracts under adverse selection and moral hazard, comparing them with those under a single informational asymmetry. The complex interactions of self-selection and moral hazard constraints have important consequences. We develop an analytic approach that allows a characterization of equilibrium and optimal (Pareto Optimal (PO), and Utilitarian optimal (UO)) allocations. Among the results : (i) a PO allocation may involve "shirking" (not only less care in accident avoidance than is possible, but less care compared to the case of pure moral hazard) either by high risk individuals in the case of single-crossing preference or by one or both types in the case of multi-crossing preference (as may naturally be the case under the double inf...
May 2013Optimal Provision of Loans and Insurance Against Unemployment From A Lifetime Perspective
with Joseph Stiglitz: w19064
In an earlier paper, we showed that integrated individual accounts, allowing individuals to borrow against future pensions when they are unemployed, can be welfare increasing, because it allows increased inter-temporal consumption smoothing without attenuating incentives to search. Here, we examine from a lifetime perspective how the optimal mix between publicly provided unemployment insurance (UI) and loans against pension accounts changes over time in a model where unemployment may occur in any period. Even loans can have an adverse effect on search, because they attenuate the consequences of unemployment; and even more so when there is a chance that the loan will not be repaid. As we present the optimal mix of loans and UI as the one that balances the adverse incentive costs with the ...
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