A severe nursing shortage in the United States contributes to an estimated 20,000 hospital deaths each year, says a new study published Wednesday in the Journal of the American Medical Association. As part of their analysis, researchers from the University of Pennsylvania surveyed 10,000 nurses at nearly 170 hospitals in the state and examined data from over 232,000 people who had checked into a hospital for routine surgery.

According to the report, when admitted to a facility with a shortage of nurses, patients' chances of dying increased by 31 percent. Nurses caring for more than four patients at one time (nurses at most understaffed hospitals cared for eight or more patients) were more prone to make a lethal mistake, such as failing to diagnose a potentially fatal complication. Overworked nurses were also found to suffer from burnout, a condition that increases the risk of misdiagnosis.

Various nursing associations contend hospitals have reduced nursing staffs in an attempt to save money. Hospital advocates, however, insist facility managers have had a difficult time in recent years filling vacancies left when nurses retire.