Landrigan was working on his own large-scale study when the 2009 Medicare study came out. His team read the hospital charts for thousands of patients from 2002 to 2007. The results, published last year, were equally sobering and showed that roughly a fifth of all hospitalized patients suffered harm from medical errors; cutting trainee work hours had no impact.

The question, then, is why? There are several possible explanations for the failure of the nationwide 80-hour rule to reduce medical harms. In 2008, the journal Pediatrics reported that two-thirds of residents regularly broke the rule, suggesting that poor enforcement, perhaps related to ingrained norms, had undercut the reform. Landrigan, one of the authors of that study, also thinks that the accreditation council did not go far enough; it had not, after all, banned being on call overnight and still allowed shifts up to 30 hours. Now that the council has abolished extended shifts, at least for first-year residents, Landrigan expects fewer errors.

And yet there are reasons to believe otherwise. About 98,000 people die every year from medical errors. Some of those mistakes are made by doctors whose judgment has been scrambled by lack of sleep. But fixating on work hours has meant overlooking other issues, like lack of supervision or the failure to use more reliable computerized records. Worse still, the reforms may have created new, unexpected sources of mistakes. Shorter shifts mean doctors have less continuity with their patients. If one doctor leaves, another must take over. Work-hour reductions lead to more handoffs of patients, and the number of these handoffs is one of the strongest risk factors for error. As a result, many hospitalized patients are at the mercy of a real-life game of telephone, where a message is passed from doctor to doctor — and frequently garbled in the process.

Ted Sectish is a no-nonsense, soft-spoken pediatrician who runs the residency program at Children’s Hospital in Boston and who has overseen residents for almost 20 years. To his mind, the fundamental problem is that most training programs fail to teach how to clearly convey vital information. “Patient handoffs are a nonstandardized process and a skill that’s not even taught,” Sectish says with dismay. (A 2006 survey found that 60 percent of residents received no training in proper handoff procedures.)

Here is a stark example of what Sectish is complaining about, from a recent study of handoffs at Yale-New Haven Hospital, in which all trainee handoffs at the hospital were recorded for two weeks and analyzed to better understand communication problems. This is a verbatim record of a trainee giving a report to the doctor coming on shift:

“O.K., so this young woman, she came in with L.F.T.’s” — liver-function tests — “in the thousands. But she also had, she had something else. O.K. Yeah, I guess it was just this. So they, I think they just think it’s viral hepatitis. I don’t know why she’s still here. I guess they’re just waiting for her L.F.T.’s to normalize again, and then they’re going to send her home.”

How was the on-shift trainee to make sense of that? Later that evening, the woman’s blood glucose rose to dangerous levels because the handoff omitted a key fact: the medicine to keep it under control wasn’t given during the day. On average, one in four sessions studied resulted in errors.

I asked Sectish if I could observe a routine shift change at Children’s Hospital, so one evening in February, I accompanied him to a small conference room near the nursing station at a general pediatrics unit. Two trainees, one going off-shift and one coming on-shift, sat next to a dry-erase board on which were listed the 12 children under the team’s care. This was a light census; some nights, trainees can manage up to 40 patients. There were no supervising doctors or nurses in the room, which is typical.