The design of Medicare Part D causes most beneficiaries to receive fragmented health insurance, with drug and medical coverage separated. Fragmentation is potentially inefficient since separate insurers optimize over only one component of healthcare spending, despite complementarities and substitutabilities between healthcare types. Fragmentation of only some plans can also lead to market distortions due to differential adverse selection, as integrated plans may use drug formularies to induce enrollment by patients that are profitable in the medical insurance market. We study the design of insurance plans in Medicare Part D and find that formularies reflect these two differences in incentives. (JEL D82, G22, H51, I13, I18, L65)
The impact of health insurance expansion on physician treatment choice: Medicare Part D and physician prescribing