We have an ER problem.

Too many people use them for routine care, and too many people use them because they're uninsured. Now, these sound like the same problem. Maybe people use emergency rooms for routine care because they don't have insurance. And maybe giving them insurance will let them get cheaper preventative care instead of more expensive ER care. That is, maybe insuring the uninsured will pay for itself!

Well, no.

Five years ago, Oregon did something that was equal parts depressing and scientific genius. It held a Medicaid lottery. See, the state had money to expand its Medicaid system, but not enough to meet all the demand for it. So they had people draw numbers. That's the depressing part. The genius part is there wasn't any difference between the uninsured people who did and didn't win Medicaid coverage. It was just luck—which is another way of saying a randomized controlled trial. That's let researchers test what getting insured does and doesn't do.

It turns out one thing getting insured does is increase ER visits. Indeed, a new paper in Science finds that people who won Oregon's Medicaid lottery went to the ER 40 percent more than people who lost it in the two years after. So much for the idea that being insured will save money by cutting down on trips to the ER.

But why are the newly-insured going to the ER more? Part of it is they no longer have to pay for it all. But, as Ray Fisman points out, part of it is that they're still going to the ER for non-emergency care. Primary-care doctors are just too busy to see every non-scheduled patient, so they refer some of these more urgent cases to the ER. In other words, more insured people means more ER trips in part because we don't have enough doctors. We need things like high-skill immigration for MDs, more urgent care clinics, and relaxed nurse practitioner licensing so they can take the lead on more cases. In fact, as Sarah Kliff reports, Oregon has already begun experimenting with ways to cut down on ER visits. One simple idea they've tried is putting community health workers in the ERs to screen out patients with chronic, and not urgent, conditions.

Our healthcare system has coverage and cost problems. It was nice—and convenient—to think fixing the former would help the latter, but it's not true. Lunch is never free, especially at the hospital.