How not to do statistics…

How not to do statistics…

How not to do statistics…

Comments Off on How not to do statistics…

Journal of the American Medical Association

In January of this year, the Journal of the American Medical Association published an analysis of 100 studies in what looked like an honest attempt to assess the relationship between body mass index and mortality. The results, a finding that moderately overweight people have a lower rate of mortality than the underweight or people of normal weight was immediately seized upon by the media and activist groups around the world leaving research group panellists protesting that…

…the popular journalism and commentary about Flegal’s research could undermine the credibility of science, citing articles that show studies wavering between alternating conclusions, and opinion pieces suggesting that researchers have some conspiratorial interest in making people feel bad about their weight or lifestyle choices.

Well, saner minds — Harvard researchers to be exact — have now looked over the research and it wasn’t an honest attempt at anything. Its statistics done at such a shoddy level any grad student in stats class would be failed for something half this bad — as, apparently, should all the organizations who claimed to review this mess…

Harvard Medical School

The selection criteria that Flegal used for her meta-analysis ruled out high-quality studies of 6 million people (more than twice as many as were represented in her analysis), said Hu. These studies, in aggregate, show that the highest survival rates are in normal-weight people, not the overweight, Hu said.

In other words, the study was designed to ignore decent research and only select small samples of the known-to-be-messed-up kind…

The studies that Flegal did use included many samples of people who were chronically ill, current smokers and elderly, according to Hu. These factors are associated with weight loss and increased mortality.

Specifically, she selected studies known to be biased in favour of weight extending life because the thin people had cancer…

In other words, people are not dying because they are slim, he said. They are slim because they are dying—of cancer or old age, for example. By doing a meta-analysis of studies that did not properly control for this bias, Flegal amplified the error in the original studies.

Then, there was no attempt to even acknowledge such much less moderate the skewing effect of such…

There is also no known biological basis for any protective effect from being overweight, the panellists said, citing studies that show a clear connection between being overweight and conditions such as hypertension and insulin resistance, which are risk factors for coronary heart disease, stroke and several cancers.

“Even as you get near the upper reaches of the normal weight range, you begin to see increases in chronic diseases,” said JoAnn Manson, chief of the Division of Preventive Medicine, Brigham and Women’s Hospital, HMS Michael and Lee Bell Professor of Women’s Health, and HSPH professor of epidemiology. “It’s a clear gradient of increase. There is no evidence here of any global protective factor for being overweight.”

This was published in the full knowledge that she could cite no actual mechanism for the supposed protection offered by extra weight — and such was not admitted either…

“There are lies, damned lies and then there are statistics…”

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