The uninsured are not responsible for overcrowding in the nation's hospital emergency departments, despite conventional wisdom to the contrary, a study out Tuesday says.

Rather, insured patients represent the majority of the increased use of the nation's emergency departments over the past decade, says the article in the Journal of the American Medical Association.

Even medical researchers get that wrong, say the study's authors, who reviewed work in medical journals and found three common misconceptions about the uninsured and their use of emergency departments.

Those myths are: The uninsured use the emergency department for non-urgent care, they are the leading cause of ER crowding and they use the ER disproportionately to their share of the population.

"I became very frustrated with the number of unsupported assertions in excellent journals," says co-author Manya Newton, an emergency physician at the University of Michigan.

The study found that a higher proportion of patients with public insurance, such as Medicaid and Medicare, use emergency departments than the uninsured.

Yet the uninsured do represent a large percentage of patients in some hospitals where the surrounding city has high levels of uninsured residents, the study says.

Research shows uninsured patients are less likely than insured patients to visit the ER for non-urgent problems, Newton says. That's partly because it costs patients so much more to go to the ER than to other types of care.

"There's a myth that the emergency department provides free care," Newton says. "Yes, we see anyone who shows up at the door, but when we see you, we will send you a bill. The uninsured don't want to pay thousands of dollars to come in for the sniffles."

The number of visits to emergency rooms nationally rose 19 percent from 1995 to 2005, even as the number of hospital ERs fell by 9 percent, the Centers for Disease Control and Prevention reports.

Overcrowding in ERs has many causes. One problem is that patients can't be moved out of emergency departments if other parts of the hospital are full or don't have enough staff, according to Newton's study and other research.

Ann O'Malley, a researcher with the non-partisan think tank Center for Studying Health System Change, says people with insurance often go to the emergency department for problems that could be handled in a doctor's office because they face long waits to see their own doctor — or need help after-hours.

"We need to strengthen access to care in the community, regardless of what type of insurance people have," O'Malley says. "It's misdirected to make the uninsured the bad guys."