In 2008, Oregon opened its Medicaid rolls to some working-age adults living in poverty, like Ms. Parris. Lacking the money to cover everyone, the state established a lottery, and Ms. Parris was one of the 89,824 residents who entered in the hope of winning insurance. With that lottery, Oregon became a laboratory for studying the effects of extending health insurance to people who previously did not have it. Health economists say the state has become the single best place to study a question at the center of debate in Washington as the Supreme Court prepares to rule, likely next week, on the constitutionality of President Obama's healthcare law: What are the costs and benefits of coverage?