When poor people are given medical insurance, they not only find regular doctors and see doctors more often but they also feel better, are less depressed and are better able to maintain financial stability, according to a new, large-scale study that provides the first rigorously controlled assessment of the impact of Medicaid.

While the findings may seem obvious, health economists and policy makers have long questioned whether it would make any difference to provide health insurance to poor people.

It has become part of the debate on Medicaid, at a time when states are cutting back on this insurance program for the poor. In fact, the only reason the study could be done was that Oregon was running out of money and had to choose some people to get insurance and exclude others, providing groups for comparison.

Some said that of course it would help to insure the uninsured. Others said maybe not. There was already a safety net: emergency rooms, charity care, free clinics and the option to go to a doctor and simply not pay the bill. And in any case, the argument goes, if Medicaid coverage is expanded, people will still have trouble seeing a doctor because so few accept that insurance.