An effort to improve patient care in the United States by shortening work shifts for new physicians has backfired, two studies show.

Patient care worsened as medical errors increased, in part because of the handoff of care from one resident physician to another after the end of a 16-hour shift. The Accreditation Council for Graduate Medical Education mandated in 2011 a maximum work shift of 16 hours for residents, a change from a 30-hour per week scheme instituted in 2003.

Researchers put the kibosh on the first study early after residents and nurses reported a dramatic drop in patient care quality. They found the incidence of handoffs from one resident to another rose 130 percent to 200 percent.

The second study, a survey report in the "Intern Health Study," showed similar trends among interns at different stages of their residency.

Most tellingly, residents said they were not getting more sleep with shortened work hours - and were experiencing the same levels of depression as interns responding before the latest change, according to Dr. Srijan Sen and colleagues at the University of Michigan at Ann Arbor.

The residents also reported equivalent levels of concern about personal well-being but were now much more worried about making errors, with 23.3 percent expressing that concern compared to 19.9 percent before the change. Also, interns who were depressed tended to commit more errors.

Sen and colleagues surveyed more than 2,300 residents from 14 university and community-based medical institutions, to make the counter-intuitive find.

"Although interns report working fewer hours under the new duty hour restrictions, this decrease has not been accompanied by an increase in hours of sleep or an improvement in depressive symptoms or well-being," researchers said, "but has been accompanied by an unanticipated increase in self-reported medical errors."

The researchers said alternative strategies must be found to improve patient care, perhaps by adopting work schedules that "account for circadian phase," in addition to spending money on additional staff members.