This is the VOA Special English Health Report.

Being a patient in certain hospitals in the month of July can be dangerous or even deadly. That was the finding of sociology professor David Phillips at the University of California, San Diego, and his student Gwendolyn Barker.

They examined more than 244,000 death records from across the United States. These were from 1979 to 2006. The researchers looked at records that listed "medication errors" as the main cause of death.

These medication mistakes included the accidental overdose of a drug or the wrong drug being given or taken. They also included accidents with the use of drugs in medical procedures or operations.

The researchers found that these mistakes caused ten percent more deaths in July than in other months. They found no similar link for other causes of death or for deaths outside hospitals.

But what makes July so deadly? The professor and his student believe they know.

They found that this ten percent increase only happened in counties with teaching hospitals. These are hospitals where new doctors, known as residents, come for more training after medical school.

Hospitals in the United States employ their newest medical residents every year in the month of ... July.

David Phillips and Gwendolyn Barker believe there is a clear link between deadly medical errors and the arrival of new residents. They also examined hospitals without residency programs. They found no unusual increase in deaths caused by drug errors.

Medical residents may stay at a teaching hospital for three years or more. They are given responsibilities for patient care. But they are not supposed to work alone. They are supervised by more experienced doctors.

The researchers say teaching hospitals should examine the responsibilities of new doctors. They also say the new residents should be supervised more closely and should be taught more about medication safety.

The researchers say if hospitals do these things, they will reduce medication errors, as well as the costs related to these mistakes.

The findings are published in the Journal of General Internal Medicine.

And that's the VOA Special English Health Report. For more health news, go to voaspecialenglish.com. You can read and listen to all of our reports and write comments. You can also write to us on Facebook and Twitter at VOA Learning English. I'm Jim Tedder.

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（来源：VOA 编辑：陈丹妮）