Characterizing Efficient Social Insurance Institutions: Theory and Computation

本研究将发展理论和计算方法来描述有效的社会保险制度。我们将社会保险机构定义为一种强制性的政府运营计划，它提供一套国家规定的税收（保费或缴款）和转移（福利），涵盖一系列明确定义的风险。一个有效的社会保险制度是以最低的成本为制度中的个人提供一定水平的福利。我们的研究将试图提供有效的社会保险制度的特征，涵盖以下风险：1)寿命，通过强制性养老金或“老年保险”；2)残疾，通过残疾保险；3)失业，通过失业保险；4)医疗保健费用，通过医疗保险。社会保险的另一个目标是收入和/或财富的终身再分配。这可以看作是针对第五类风险的保险，即针对具有某些固定特征或“类型”的个人的保险，这些特征或“类型”可能导致终身就业、收入、财富和福利的永久性降低。在发达经济体，社会保险项目规模庞大且无处不在。在美国，社会保障（老年、残疾和失业保险）、医疗保险、医疗补助的支出占联邦总支出的48.3%，2000年占GDP的9.8%（美国国会预算办公室）。所有的预测都表明，除非减少福利，否则随着婴儿潮一代步入老年并开始退休，社会保险支出将在未来几十年迅速增长。虽然有人建议通过各种“私有化”计划将社会保险的成本从政府转移到私营部门，但各种道德风险和逆向选择问题阻碍了私营保险市场的运作。我们把市场的不完全性作为政府强制提供保险的主要理由，并作为我们分析的基本出发点。我们假设政府可以强制全民参与，但我们也假设它面临与私人保险机构一样的信息约束，如果它们存在的话。我们通过两种截然不同但相关的策略来处理这些基本的信息不对称：1)“动态机制设计”（DMD）方法，即在满足一定参与约束和激励约束的所有可能政策的无限维空间中寻找有效的政策；2)“参数机制设计”（PMD）方法，即在忽略激励约束的有限维社会保险制度子空间中搜索“近似有效”的社会保险制度。使用这些技术，我们不仅能够表征有效的社会保险机构的形式，我们还能够量化当前社会保险机构的低效率程度。作为对美国和其他发达经济体社会保险的全面、综合分析的一部分，我们希望能够描绘出最优社会保障和残疾保险计划的特征。考虑到社会保险在GDP中所占的很大份额，发现更有效的社会保险计划所带来的潜在成本节约为本研究提供了强有力的、实用的理由。

This research will develop theoretical and computational approaches for characterizing efficient social insurance institutions. We define a social insurance institution as a compulsory government-run program that provides a set of state-contingent taxes (premiums or contributions) and transfers (benefits) that cover a well-defined set of risks. An efficient social insurance institution is one that provides a given level welfare to the individuals in the system at minimal cost. Our research will attempt to provide characterizations of efficient social insurance institutions that cover the following risks: 1) longevity, via mandatory pensions or "old age insurance", 2) disability, via disability insurance, 3) unemployment, via unemployment insurance, and 4) health care costs, via medical insurance. Another objective of social insurance is lifetime redistribution of income and/or wealth. This can be viewed as insurance for a fifth class of risks, namely insurance for individuals who have certain fixed characteristics or "types" that may lead to permanently lower lifetime employment, earnings, wealth, and welfare.Social insurance programs are large and pervasive in developed economies. In the U.S., spending on Social Security (Old Age, Disability, and Unemployment Insurance), Medicare, Medicaid amounted to 48.3\% of total Federal spending and 9.8\% of GDP in 2000 (U.S. Congressional Budget Office). All forecasts indicate that unless benefits are reduced, social insurance spending will grow rapidly over the coming decades as the baby boomers age and start to retire. Although there have been proposals to shift the costs of social insurance from the government to the private sector via various "privatization" schemes, a variety of moral hazard and adverse selection problems hinder the operation of private insurance markets. We take market incompleteness as the principal rationale for mandatory government provision of insurance, and as the basic point of departure for our analysis. We assume that the government can compel universal participation, but we also assume that it faces the same informational constraints as private insurance institutions would face if they existed. We deal with these fundamental informational asymmetries via two very different but related strategies: 1) a "dynamic mechanism design" (DMD) approach where we search for an efficient policy over an infinite-dimensional space of all possible policies that satisfy certain participation and incentive constraints, and 2) a "parametric mechanism design" (PMD) approach where we search for an "approximately efficient" social insurance institution in a finite-dimensional subspace of social insurance institutions and where incentive constraints are ignored.Using these techniques we will not only be able to characterize the form of efficient social insurance institutions, we will also be able to quantify the degree of inefficiency in current social insurance institutions. We expect to be able to characterize optimal social security and disability insurance programs as part of a comprehensive, integrated analysis of social insurance in the U.S. and other developed economies. Given the large share of GDP devoted to social insurance, the potential cost savings from discovering more efficient social insurance programs provides a strong, practical rationale for this research.