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

We analyze the impact of expanded adult Medicaid eligibility on the enrollment of already-eligible children. We analyze the 2008 Oregon Medicaid lottery, in which some low-income uninsured adults were randomly selected to be allowed to apply for Medicaid. Children in these households were eligible for Medicaid irrespective of the lottery outcome. We estimate statistically significant but transitory impacts of adult lottery selection on child Medicaid enrollment: at three months after the lottery, for every 9 adults who enrolled in Medicaid due to winning the lottery, one additional child also enrolled. Our results shed light on the existence, magnitude, and nature of so-called "woodwork effects".