A major new study on Medicaid just became public. I know—nothing excites readers more than the phrase “major new study on Medicaid.” Bear with me. This study is already getting a lot of attention: Conservatives and libertarians are citing it as evidence that expanding Medicaid is wrong. That has me wondering: Did they read read the same study that I did?

By now, you're probably familiar with the controversy over the Medicaid expansion. Under Obamacare, the federal government will provide states with money to expand eligilibty for the program, so that anybody with an income at or just above the poverty line can enroll. But states have the option to decline the money. Many states seem likely to do that, at least for the short term. Among them are Florida and Texas, two large states with large numbers of uninsured residents. Several million Americans—nearly 2 million in Texas alone—will lose out on health insurance unless officials in those states have a change of heart.

The common element in states declining to participate is that they are all states in which Republicans have leverage: Either a Republican governor or a Republican-controlled house of the legislature, or both, opposes the expansion. And one reason, obviously, is cost: These officials don’t want their states paying more for Medicaid, even if the amounts are minimal and they’d come out ahead because of savings elsewhere in their budgets. But Republicans and their allies frequently make another argument—that the program doesn’t do much good. Some go farther, and argue that people on Medicaid actually end up worse off than people with no insurance at all.

That’s where the new study comes in. Opponents of the expansion think the results back up their arguments. The Cato Institute's Michael Cannon, for example, says the study " throws a huge 'STOP' sign in front of ObamaCare’s Medicaid expansion." I think they are reading very selectively. The evidence does call into question one important claim liberals have made about Medicaid—and liberals who make that claim need to start qualifying it. But the study validates two other arugments that defenders of Medicaid make. Both of these arguments are equally important.

The study appears in the New England Journal of Medicine. The two principal investigators are a pair of highly respected economists—Katherine Baicker, from Harvard, and Amy Finkelstein, from the Massachusetts Institute of Technology. They are leading up a team of similarly qualified experts, among them two scholars familiar to readers of this space: Jonathan Gruber (at MIT) and Joseph Newhouse (at Harvard). But the significance of this study is not the authors. It’s the design, which came about thanks to a unique circumstance in Oregon. A few years ago, the state had enough funding to open up its Medicaid program to 10,000 people—and many times that number who wanted the insurance. The state decided the only fair way to distribute the coverage was by lottery.