·  ·    The ACA left the important decision of whether to create a state-based marketplace or not up to the states, and the Supreme Court gave states the option to expand Medicaid or not.  

Fifteen states (representing about one-third of the uninsured in the U.S.) have chosen to create state-based marketplaces, 10 states are using the federally-facilitated marketplaces (FFM) but are expanding Medicaid, while the remaining 26 states have chosen to use the federally-facilitated marketplace and are not expanding Medicaid (to date).

Based on findings from this author (Timothy McBride, Brown School, Washington University in St. Louis), in the first five months of the open enrollment period, an uninsured person in the states that have implemented the state-based marketplaces is more than twice as likely to have either chosen a marketplace plan or been determined eligible for Medicaid, as compared to the uninsured in states that are using the federally-facilitated marketplace.  Read the brief available here.