PORTLAND, Ore. (AP) - A lottery system created to decide who receives insurance through the Oregon Health Plan is offering researchers a rare chance to study the benefits of health coverage.

By tracking insured and uninsured Oregonians, researchers hope to test how health insurance affects a person's access to care, doctor visits, hospital stays and trips to the emergency room.

The Oregonian newspaper said that researchers also plan to look at how health insurance affects physical and mental health, chronic illnesses, disabilities, pain, financial stress and quality of life.

"For a health policy researcher, this is the opportunity of a lifetime, said Katherine Baicker, a health economist at the Harvard School of Public Health and a leader of the Oregon study. "This is much bigger than anything Ive ever worked on."

Randomized, controlled studies in which a large group is divided into two otherwise equal groups to test a treatment are ideal for scientific research.

Randomized studies, however, are often impossible in public policy research because forcing someone someone to go without treatment simply to test a result is unethical, said Heidi Allen, a researcher with the Center for Outcomes Research and Education at Providence Health & Services in Portland.

Oregon offered a chance for Allen and other researchers to test policy because the budget forced the state to turn to a lottery to offer benefits to people who do not have or cannot afford health insurance.

The lottery began last year after enrollment in the Oregon Health Plan standard benefit package was frozen for four years.

The state provided coverage for another 10,000 Oregonians chosen randomly in the lottery, but some 100,000 people applied for the benefits.

The state also agreed to share a list of applicants coded by number - not by name - if the researchers raised the necessary grant money and agreed to work with local partners, including Portland State University and Providence.