The Oregon Health Study has won academic attention both because of the pedigree of the researchers — including Joseph P. Newhouse, who designed the renowned RAND Health Insurance Experiment in the 1970s, and Amy Finkelstein, the most recent winner of the John Bates Clark Medal, an economic prize considered second only to the Nobel — and the distinct nature of the state’s health-insurance lottery. By assigning coverage randomly, Oregon gave researchers more confidence that they had teased out the true effects of insurance, and had not been fooled by other differences between the insured and the uninsured.

“The study put to rest two incorrect arguments that persisted because of an absence of evidence,” said Katherine Baicker, a Harvard economist who worked on the study and served as an economic adviser to President George W. Bush.

“The first is that Medicaid doesn’t do anything for people, because it’s bad insurance or because the uninsured have other ways of getting care,” Ms. Baicker said. “The second is that Medicaid coverage saves money” by increasing preventive care, for instance.

“It’s up to society to determine whether it’s worth the cost,” she added.

Discussions with 17 insured and uninsured participants in the Oregon Health Study illuminated how coverage changed and did not change their lives. Many described poverty and its attending problems, not health care, as their major challenge. (The Affordable Care Act, President Obama’s health care law, requires states, in 2014, to extend Medicaid eligibility to all adults within 133 percent of the poverty line, which is currently $11,170 for a household of one and $23,050 for a household of four.) A handful said that they were not overly bothered by their lack of coverage, or that winning Medicaid had not had much of an effect.

But many, including Ms. Parris and Mr. Bell, said that Medicaid had made a significant — even transformative — difference in their lives.

Ms. Parris got surgery for her foot, and additional care. She is also getting spinal surgery. Doctors have helped her address her depression, triggered by the death of one of her children. Her weight has come back down, and her mobility is far better. “It saved my life,” she said.