Evolving Choice Inconsistencies in Choice of Prescription Drug Insurance
We explore choice inconsistency over time within the Medicare Part D Prescription Drug Program. Using the full universe of Part D claims data, we revisit our earlier work on partial data to replicate our results showing large “foregone savings” among Part D enrollees. We also document that this foregone savings increases over time during the first four years of the Part D program. We then develop a rich dynamic structural framework that allows us to mathematically decompose the “foregone welfare” from inconsistent plan choices into components due to demand side factors, supply side factors, and changes in preferences over time. We find that the welfare cost of choice inconsistencies increases over time. Most importantly, we find that there is little improvement in the ability of consumers to choose plans over time; we identify and estimate little learning at either the individual or cohort level over the years of our analysis. Inertia does reduce welfare, but even in a world with no inertia we estimate that substantial welfare losses would remain. We conclude that the increased choice inconsistencies over time are driven by changes on the supply side that are not offset both because of inertia and because non-inertial consumers still make inconsistent choices.