The Oregon Health Study upended a lot of conventional thinking about health insurance. The study made use of a 2008 state lottery that randomly assigned some low-income Oregon residents to get insurance from Medicaid and others to remain uninsured. Then it followed them for two years to see what happened.

Among the study’s surprising findings: Patients who got insurance used the emergency room more often than their uninsured peers, undermining a common argument in favor of expanded insurance coverage. People who got Medicaid also had a much easier time finding doctors, countering views held by the programs’ critics that Medicaid can be worse than no insurance. There were some important questions the study never answered: It didn’t find any evidence that patients’ physical health improved over the two years.

Managing the study involved gathering a lot of data about the participants — surveying them on their happiness and financial health, examining their health records and looking at whether they were getting calls from debt collectors. The researchers have published their empirical findings in medical and economics journals — there’s a summary with links here. More recently, Heidi Allen, a member of the team, has gone back and collected interviews with the study’s subjects. They’ve been struck by just how compelling individual stories can be — even now, when they know the “right” answer.

“If you look at them, some people do say the exact opposite of what we found,” said Amy Finkelstein, a professor at M.I.T., who helped lead the Oregon study. “From a randomized controlled trial, you can see something that wasn’t at all what you were looking for.”