Optimal Health Insurance and the Distortionary Effects of the Tax Subsidy

This paper introduces a model of optimal health insurance. This model provides theoretical guidance of the relationship between household preferences, cost-sharing, and premiums. I apply this model to understand how the income tax subsidy distorts optimal cost-sharing in health insurance. Typically, insurance protects individuals from financial risk. Health insurance plans, however, are frequently designed to provide coverage at non-catastrophic levels of financial loss. The presence of a health insurance subsidy in the United States tax code, which enables individuals to pay premiums in pre-tax dollars, encourages the purchase of more generous health insurance plans. Little is known about how the tax subsidy affects preferences for the structure of costsharing in private plans. This model illustrates how the tax subsidy can distort the optimal cost-sharing schedule. The model is tested empirically using claims data in the Medical Expenditure Panel Survey and a regression discontinuity strategy that uses discrete changes in the marginal tax rate at the Social Security taxable maximum for identification.