Out of the Woodwork: Enrollment Spillovers in the Oregon Health Insurance Experiment

We analyze the impact of expanded adult Medicaid eligibility on the Medicaid enrollment of already-eligible children. To do so, we exploit the 2008 Oregon Medicaid lottery, in which some low-income uninsured adults were randomly selected for the chance to apply for Medicaid. Children in these households were eligible for Medicaid irrespective of whether the household won the lottery. We estimate statistically significant but transitory impacts of adult lottery selection on children’s Medicaid enrollment: for every 9 adults who enroll in Medicaid due to the lottery, one additional child also enrolls at the same time. Our results shed light on the existence, magnitude, and nature of so-called “woodwork effects”.