How Managed Care Affects Medicaid Utilization : A Synthetic Difference-in-Differences Zero-Inflated Count Model

We develop a synthetic difference-in-differences statistical design to apply to experimental data for adult women living in Hennepin County, Minnesota, to estimate the impact of Medicaid managed care on various modes of medical care use. Because the outcomes of interest are utilization counts with many persons using none of a particular mode of care we use count regression models that are adjusted for excessive zeros. We find no reductions in physician visits or hospital inpatient and emergency department care use, but reductions in hospital outpatient care. Simulations designed to judge the economic significance of our results suggest a program effect that is a savings of about ten percent