Medicaid, the government program for providing health insurance to low-income and disabled Americans, is the largest health insurer in the United States with more than 73 million enrollees. It is also the sector of the U.S. public health insurance system that relies most heavily on the tools of...

Health insurers increasingly compete on their covered networks of medical providers. Using data from Massachusetts' pioneer insurance exchange, I find substantial adverse selection against plans covering the most prestigious and expensive "star" hospitals. I highlight a theoretically distinct...

Some consumers lack the cash needed to pay for medical care. As a result, they either delay care until they can pay for it or they forgo the care altogether. To test for such a possibility, we study the distribution of monthly Social Security checks among Medicare Part D enrollees. When Social...

We leverage two unique natural experiments to show that, in public drug insurance for the low-income elderly in the U.S., defaults have large and persistent effects on plan enrollment and beneficiary drug utilization. We estimate that when a beneficiary's default is exogenously changed from one...

In this essay, we review the theory and evidence concerning selection in competitive health insurance markets and discuss the common policy tools used to address the problems it creates. We begin by outlining some important but often misunderstood differences between two types of conceptual...

In most US health insurance markets, plans face strong incentives to "upcode" the patient diagnoses they report to the regulator, as these affect the risk-adjusted payments plans receive. We show that enrollees in private Medicare plans generate 6% to 16% higher diagnosis-based risk scores than...

High administrative costs in U.S. health care have provoked concern among policymakers over potential waste, but many of these costs are generated by managed care policies that trade off bureaucratic costs against reductions in moral hazard. We study this trade-off for prior authorization...

Existing research on selection in insurance markets focuses on how adverse selection distorts prices and misallocates products across people. This ignores the distributional consequences of who pays the higher prices. In this paper, we show that the distributional incidence depends on the...