Revisiting the effects of state earned income tax credits on infant health: a quasi-experimental study using contiguous border counties approach

Background To examine the effects of refundable state earned income tax credits (EITC) on infant health. Methods We use the restricted-access U.S. birth certificate data with county codes from 1989 to 2018. Birth outcomes include birth weight, low birth weight, gestational weeks, preterm birth, and the fetal growth rate. The analytical sample includes single mothers with high school education or less. Two specifications of two-way fixed effects models are employed. The first specification accounts for shared time trends across all states/counties. The second specification estimates effects based on EITC changes within contiguous counties across state borders which accounts for contemporaneous events specific to each contiguous county pair. Models are estimated pooling and stratifying by parity subgroups. Results Under the first specification, refundable state EITC is associated with improved birth outcomes. Pooling all parity, a 10%-point increase in refundable EITC is associated with an 8-gram increase in birth weight (95% CI: 2.9,14.6). The effect increases by parity. In contrast, the estimates from the second model are much smaller and statistically non-significant, both pooling and stratifying by parity. Conclusions Comparing contiguous counties across state borders, there is no evidence that refundable state EITC affects birth outcomes. However, the estimates still do not rule out moderate to large benefits for third or higher born infants.