Whoops - the New England Journal of Medicine paper has been retracted. From National Public Radio by way of Retraction Watch:
Errors Trigger Retraction Of Study On Mediterranean Diet's Heart Benefits
Ask just about anybody, and you'll probably hear that a healthy diet is one full of fruits and vegetables, olive oil, nuts and fish — what's called Mediterranean diet. A lot of research has suggested people who eat this way tend to be healthier, but it's been harder to prove whether that is because of the diet or some other factor.
So in 2013, many took notice of a study in the New England Journal of Medicine that seemed to provide some proof. The study found that people eating the Mediterranean diet supplemented with olive oil were 30 percent less likely to experience a heart attack, stroke, or death from cardiovascular causes than people assigned to a low-fat diet. People who stuck with a Mediterranean diet supplemented with mixed nuts had a 28 percent lower risk than those asked to follow a low-fat diet.
The results got wide media attention, including from NPR.
But the New England Journal of Medicine retracted the paper Wednesday because of problems in the way the study was carried out.
It was a problem with the randomization of the data:
It turns out approximately 14 percent of the more than 7,400 study participants hadn't been assigned randomly to either the Mediterranean diet or a low-fat one. When couples joined the study together, both had been picked to follow the same diet. At one of the 11 participating study sites, the lead investigator had assigned the same diet to an entire village and didn't tell the rest of the investigators.
Oops - a lot of work went out the window just to make things easier for the participants.
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