The Effect of Medicaid Expansion on Patient Flow in the Emergency Department

Abstract

We study the effect of Medicaid expansion on the patient flow in Emergency Department (ED) using the difference-in-difference approach, where the treatment group are the states that expanded the Medicaid program at the beginning of 2014 and the control group are the states that did not expand the program between 2012 and 2016. We first focus on the average effect and find that Medicaid expansion increases outpatient ED length of stay by 3.1% (or 4.7 minutes), inpatient ED length of stay by 2.5% (or 7.5 minutes), wait time by 11.1% (or 3.6 minutes), and boarding time by 4.1% (or 4.9 minutes). We then apply the causal forest approach to study the treatment effect heterogeneity and find that the effect of Medicaid expansion varies widely across different hospitals. Finally, we use a two-station queueing model to characterize the patient flow in emergency and inpatient departments and analyze how much bed capacity or service rate increase is needed in order to offset the increase of wait time and boarding time due to Medicaid expansion.