BBC News is running a medical care story today 
that has implications for U.S. medical care. Residents who are put on a shorter 48 hour/week limit, in accordance with European Union regulations, made 33 percent fewer medical errors than those on a schedule of up to 56 hours a week. The sample size of National Health Service doctors was small but the results were significant. Thanks to Dr. Elisabeth Paice for the link.
The relevance of the study for the United States is that U.S. hospital residents are expected to work up to 80 hours a week during their training. The New York-based Commonwealth Fund has shown that patient-reported medical errors are the highest in the United States in a study comparing it with five other countries -- Australia, Canada, Germany, New Zealand and the UK. Of the six countries, the UK had the fewest patient-reported medical errors.
The new study is reported in the Quarterly Journal of Medicine. The sample size was 19 junior doctors in residence.
[N]ine studied while working an intervention schedule of
The results showed significantly lower error rates for the doctors on the new rota with fewer hours:
Average scheduled work hours were significantly lower on the intervention schedule [43.2 (SD 7.7) (range 26.0-60.0) vs. 52.4 (11.2) (30.0-77.0) h/week; P < 0.001], and there was a non-significant trend for increased total sleep time per day [7.26 (0.36) vs. 6.75 (0.40) h; P = 0.095]. During a total of 4782 patient-days involving 481 admissions, 32.7% fewer total medical errors occurred during the intervention than during the traditional rota (27.6 vs. 41.0 per 1000 patient-days, P = 0.006), including 82.6% fewer intercepted potential adverse events (1.2 vs. 6.9 per 1000 patient-days, P = 0.002) and 31.4% fewer non-intercepted potential adverse events (16.6 vs. 24.2 per 1000 patient-days, P = 0.067). Doctors reported worse educational opportunities on the intervention rota.
UPDATE: BBC has a followup story that shows old habits die hard. The story is headlined "Medics get working hours opt-out":
The government has said not all doctors will have their working week cut to 48 hours in August as planned. Ministers said the European Working Time Directive limit would not have to apply to certain doctors working in emergency medicine, or in rural areas. Instead, they will remain able to work up to 52 hours a week. Doctors' associations, which had said the shorter week did not allow enough training time, welcomed the move, but said it did not go far enough.