By Andrew Stocking, James Baumgardner, Melinda Buntin, and Anna Cook
Most beneficiaries of Medicare's Part D prescription drug insurance choose among private drug plans to receive their coverage. This paper is the first to examine the relationship between the number of competing plan sponsors and the cost of Part D during the program's first five years. Over the period from 2006 to 2010, regional Part D markets contained between 16 and 22 plan sponsors offering stand-alone plans. Consistent with economic theory, we find that increases in the number of plan sponsors within a market were associated with lower bids and lower overhead and profits of plans in that market. For example, among stand-alone plans that were not eligible to be assigned low-income beneficiaries, we find that each additional plan sponsor entering an 18-firm market was associated with a reduction in bids for a month of basic coverage to a beneficiary of average health of 0.4 percent—or $0.33 for a plan that bid $85—which corresponds to an elasticity of -0.071. (That result is an arithmetic average across six specifications in which estimates range from $0.20 to $0.50.) Because bids are used to directly determine government spending, we estimate that an additional plan sponsor nationwide was associated with a reduction in government spending of $7 million to $17 million each year.