Back during the debate over the Affordable Care Act, some of its critics questioned whether extending health insurance to the uninsured would affect their health outcomes. Even a few bishops, as I recall, suggested that the right to health care found in Catholic social teaching did necessarily require the provision of insurance.One of the problems in studying this question is that you can't just compare people with insurance to people without it, even if you control for income. There are lots of other differences that are hard to quantify. However, a few years ago Oregon was in the position of being able to extend health insurance to some--but not all--families who wanted it. They used a lottery to pick 10,000 of the 90,000 who applied. Researchers at the National Bureau of Economic Research took advantage of this random assignment to test the impact of having insurance. The results are in:

In its first year of data collection, the study found a long list of differences between the insured and uninsured, adding up to an extra 25 percent in medical expenditures for the insured.

Those with Medicaid were 35 percent more likely to go to a clinic or see a doctor, 15 percent more likely to use prescription drugs and 30 percent more likely to be admitted to a hospital. Researchers were unable to detect a change in emergency room use.

Women with insurance were 60 percent more likely to havemammograms, and those with insurance were 20 percent more likely to have theircholesterolchecked. They were 70 percent more likely to have a particular clinic or office for medical care and 55 percent more likely to have a doctor whom they usually saw.

The insured also felt better: the likelihood that they said their health was good or excellent increased by 25 percent, and they were 40 percent less likely to say that their health had worsened in the past year than those without insurance.

The study also found that those with insurance were 25% less likely to have an unpaid bill sent to a collection agency and were 40% less likely to borrow money or fail to pay bills because they had medical bills.