evidence: As of summer 2018, 17 states have chosen not to expand Medicaid. However, some are considering placing a portion of or all newly eligible individuals into private insurance. Even some expansion states are considering similar changes, arguing that private plans may produce better quality at a lower cost to the state. Yet, numerous studies comparing the effects of Medicaid versus private coverage have been confounded by selection bias: people who are able to access private insurance differ from those who qualify for Medicaid in observable and unobservable ways. So there remains little evidence on how public and private coverage compare in their effects on low-income adults. [...] It is plausible that private insurance–with broader provider networks, higher reimbursement, and market-based competition–may produce better outcomes than Medicaid. Alternatively, Medicaid may be uniquely designed to provide appropriate health care to low-income adults, who differ in significant ways from the customers typically served by commercial plans. This analysis seeks to shed light on the value of Medicaid versus other coverage types, with important implications for state expansion approaches, as well as the debate over whether to include a public option in the ACA Marketplaces. In an article recently published in JAMA Network Open, Heidi Allen, Sarah H. Gordon, Dennis Lee, Aditi Bhanja and Benjamin D. Sommers use data from Colorado to compare individuals with similar incomes across coverage types, highlighting the key differences between Medicaid and Marketplace insurance.