In a Washington Post report on the study, Ashish Jha, professor of health policy at the Harvard School of Public Health, says, "If we had a treatment that lowered mortality by 0.4 percentage points or half a percentage point, that is a treatment we would use widely. We would think of that as a clinically important treatment we want to use for our patients."

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The study was based on an analysis of 1.5 million hospital visits over a period of four years of Medicare data for elderly patients aged 65 and older, between January 2011 and December 2014; their illnesses included pneumonia, heart failure, intestinal bleeding, urinary infections and lung disease.

Researchers found that patients treated by a female doctor were less likely, by a little less than half of a percentage point, to die within a month of being hospitalized. A similar drop occurred in the likelihood of patients having to go back to the hospital over that month.

Studies in years past have indicated women practice medicine differently than men, are more likely to stick with clinical guidelines and to talk to patients about preventive care. They're also more communicative.

And while this latest study can't prove the determining factor for the increased survival rate among elderly patients is a female doctor, researchers adjusted for a number of factors to see whether other explanations could account for the difference.

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But survival rates were higher and rehospitalization rates were lower for patients with female doctors. While the differences were small — about 11 percent of patients treated mostly by women died within 30 days of entering the hospital, compared with 11.5 percent of those treated by men — it's notable that the all-male research team estimated that if male physicians' care was on a par with female physicians', 32,000 more U.S. patients a year would survive than is currently the case.