Preliminary reports from rapid-turnaround surveys have described a decline in the uninsured rate since the fall of 2013, when open enrollment began.2-5 However, numerous factors, including the economy, survey sampling error, and preexisting trends, can affect estimated rates of Americans without insurance. More generally, the systemic changes brought by the ACA pose a particular challenge for identifying the effect of the law, owing to the lack of a control group. Although to date 24 states have not expanded Medicaid, the ACA has major implications for these states, owing to subsidized marketplace coverage, the individual mandate, and a streamlined application process for uninsured persons who were previously eligible for Medicaid.6 An additional question is how quickly any coverage changes will lead to improved access to care.