作者：James A. Mirrlees，William Vickrey
国籍：U.K，USA
出处：Press Release - The Sveriges Riksbank (Bank of Sweden) Prize in Economic Sciences in Memory of Alfred Nobel，8 October 1996
For a long time, a well-known problem in connection with insurance is that damage to insured objects depends not only on external factors such as weather and attempted theft, but also on the care taken by the policyholder, which is costly for an insurance company to monitor. Corresponding problems also arise regarding different kinds of social insurance, such as health and disability insurance. Generous insurance coverage can exaggerate risktaking and affect the way individuals care for themselves and their property. Many other two-party relations involve an outcome that is observable to both parties, where the outcome depends on one party's (the agent's) actions, which cannot be observed by the other party (the principal), as well as on a random variable. In the relation between the owner and the management of a firm, for instance, the action would be the executive's work effort, the outcome would be the firm's profit and the random variable could be the firm's market or production conditions. The owners of both the insurance company and the firm want to choose terms of compensation, a "contract", which gives the agent incentives to act in accordance with the principal's interests, for example, by maximizing the owner's expected profits.
The technical difficulties encountered in analyzing these so-called moral hazard problems are similar to the income tax problems emphasized by Vickrey and solved by Mirrlees. In the mid-1970s, by means of an apparently simple reformulation of the problem, Mirrlees paved the way for an increasingly powerful analysis. He noted that an agent's actions indirectly imply a choice of the probabilities that different outcomes will occur. The conditions for the optimal terms of compensation thus provide "probability information" about the agent's choice and the extent to which insurance protection has to be restricted in order to provide the agent with suitable incentives. In designing an incentive scheme, the principal has to take into account the costs of giving the agent incentives to act in accordance with the principal's interests. The higher the agent's sensitivity to punishment and the larger the amount of information about the agent's choice contained in the outcome, the lower these costs. This is stipulated in a contract; the agent bears part of the cost of undesirable outcomes or receives part of the profits from favorable outcomes. The policyholder takes care of the insured object almost as if it were uninsured, and the executive manages the firm almost as if it were his own.
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