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Moral Hazard and Efficiency in General Equilibrium with Anonymous Trading

  • Daron Acemoglu
  • Alp Simsek

A 'folk theorem' originating, among others, in the work of Stiglitz maintains that competitive equilibria are always or 'generically' inefficient (unless contracts directly specify consumption levels as in Prescott and Townsend, thus bypassing trading in anonymous markets). This paper critically reevaluates these claims in the context of a general equilibrium economy with moral hazard. We first formalize this folk theorem. Firms offer contracts to workers who choose an effort level that is private information and that affects worker productivity. To clarify the importance of trading in anonymous markets, we introduce a monitoring partition such that employment contracts can specify expenditures over subsets in the partition, but cannot regulate how this expenditure is subdivided among the commodities within a subset. We say that preferences are nonseparable (or more accurately, not weakly separable) when the marginal rate of substitution across commodities within a subset in the partition depends on the effort level, and that preferences are weakly separable when there exists no such subset. We prove that the equilibrium is always inefficient when a competitive equilibrium allocation involves less than full insurance and preferences are nonseparable. This result appears to support the conclusion of the above mentioned folk theorem. Nevertheless, our main result highlights its limitations. Most common-used preference structures do not satisfy the nonseparability condition. We show that when preferences are weakly separable, competitive equilibria with moral hazard are constrained optimal, in the sense that a social planner who can monitor all consumption levels cannot improve over competitive allocations. Moreover, we establish ε-optimality when there are only small deviations from weak separability. These results suggest that considerable care is necessary in invoking the folk theorem about the inefficiency of competitive equilibria with private information.

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Paper provided by David K. Levine in its series Levine's Working Paper Archive with number 661465000000000232.

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Date of creation: 08 Oct 2010
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Handle: RePEc:cla:levarc:661465000000000232
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  1. Citanna, Alessandro & Villanacci, Antonio, 2002. "Competitive equilibrium with moral hazard in economies with multiple commodities," Journal of Mathematical Economics, Elsevier, vol. 38(1-2), pages 117-147, September.
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  5. Alberto Bisin & John Geanakoplos & Piero Gottardi & Enrico Minelli & Herakles Polemarchakis, 2010. "Markets and contracts," Economics Working Papers ECO2010/29, European University Institute.
    • Alberto Bisin & John Geanakoplos & Piero Gottardi & Enrico Minelli & Heracles Polemarchakis, 2009. "Markets and Contracts," Working Papers 0915, University of Brescia, Department of Economics.
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  8. Mikhail Golosov & Narayana Kocherlakota & Aleh Tsyvinski, 2002. "Optimal Indirect and Capital Taxation," Levine's Working Paper Archive 391749000000000449, David K. Levine.
  9. Jewitt, Ian, 1988. "Justifying the First-Order Approach to Principal-Agent Problems," Econometrica, Econometric Society, vol. 56(5), pages 1177-90, September.
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  11. Atsushi Kajii & Antonio Villanacci & Alessandro Citanna, 1998. "Constrained suboptimality in incomplete markets: a general approach and two applications," Economic Theory, Springer, vol. 11(3), pages 495-521.
  12. Piero Gottardi & Belén Jerez, 2007. "Comment on "Bertrand and Walras Equilibria under Moral Hazard"," Journal of Political Economy, University of Chicago Press, vol. 115(5), pages 893-900, October.
  13. Bisin, Alberto & Gottardi, Piero, 1999. "Competitive Equilibria with Asymmetric Information," Journal of Economic Theory, Elsevier, vol. 87(1), pages 1-48, July.
  14. Jerez, Belen, 2003. "A dual characterization of incentive efficiency," Journal of Economic Theory, Elsevier, vol. 112(1), pages 1-34, September.
  15. Alberto Bisin & Piero Gottardi, 2006. "Efficient Competitive Equilibria with Adverse Selection," Journal of Political Economy, University of Chicago Press, vol. 114(3), pages 485-516, June.
  16. Bisin, Alberto & Guaitoli, Danilo, 1998. "Moral Hazard and Non-Exclusive Contracts," CEPR Discussion Papers 1987, C.E.P.R. Discussion Papers.
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