Hospital emergency departments are notorious for their long waiting times. But the problem is worse than previously thought, a Yale study found.

Patients who visited the slowest 25 percent of emergency departments waited on average two hours longer than those who visited the fastest 25 percent of emergency departments, the study revealed. In addition, only 25 percent of hospitals in the study admitted 90 percent of their emergency department patients within four hours.

The report, published Oct. 5 in Annals of Emergency Medicine, found that in a typical emergency department, one-third of severely ill patients waited longer than recommended at triage for treatment. One-fourth of admitted patients spent over six hours waiting for an inpatient bed.

Yale School of Public Health professor Elizabeth Bradley GRD ’96 , graduate student Jeremy Green SPH ’13 and Yale School of Medicine professor Leora Horwitz MED ’06 analyzed data from 36,000 visits to 364 non-federal U.S. hospital emergency departments. The results came as a surprise, Bradley said.

“The people who were told they need to be seen immediately or within the first 15 minutes — that was the group that was the least likely to be seen within their target time,” Bradley said.

She said that if the government mandated that hospitals publicize records of their emergency departments’ waiting times, it would force hospitals to be more efficient.

But faster treatment of patients, Bradley added, is not a guarantee for better quality of care. Part of the problem stems from the fact that hospitals do not properly address the problems plaguing their emergency departments, said Ian Schwartz, an emergency department medical director at Yale-New Haven Hospital.

“The hospital collectively makes a decision when things are overcrowded to put that risk in the emergency department,” Schwartz said. “So essentially all the overflow of the hospital sits in the emergency room.”

Crowded emergency departments are a part of everyday life at Yale-New Haven, two medical directors at the hospital said. EMS Medical Director Carin Van Gelder said the lack of access to primary care doctors affects treatment times at Yale-New Haven. But the Yale-New Haven emergency department, unlike others, never sends ambulances to a different hospital, she added.

The physical size of Yale-New Haven is also a major issue, Schwartz said. The emergency department, which was built around 20 years ago, cannot accommodate the 200 patients that come in daily, he added.

Still, Schwartz said, the average wait time at Yale-New Haven — which varies by day and according to how urgently patients need to be seen — is around one hour, which is shorter than the wait time at a typical urban hospital.

Schwartz added that there are plans to double the capacity of the Yale-New Haven emergency department.

The data for the report came from numbers published in 2006 by the Center for Disease Control.