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The answer: 40 out of 50, a list including salt, flour, parsley and even sugar. "Is everything we eat related to cancer?" they then asked, ironically, in their article published in 2013.
Their question concerns a known but persistent problem in the world of research: too many studies use samples too small to reach generalizable conclusions.
But the pressure weighing on researchers the competition between journals and the insatiable appetite of media for studies announcing revolutions or major discoveries, causes these articles to continue to be published.
" The majority of published articles, even in serious journals, are bad ," says one of the authors, John Ioannidis, professor of medicine at Stanford, de facto specializing in the study of studies
This defender of bad scientific research demonstrated in 2005 in a resounding article " Why most published studies are false ".
Since then, he says, only some progress has been made.
Some journals require that authors provide their raw data and publish their protocol in advance. This transparency makes it possible to prevent researchers from triturating their methods and data in order to find a result, whatever it may be. They allow others to verify or " replicate " study.
Because when they are redone, experiments end seldom to the same results. Only a third of 100 studies published in the three most prestigious psychology journals were reproduced by researchers in an badysis published in 2015.
The medicine the epidemiology the clinical trials of drugs and … the nutrition studies did not do much better , insists John Ioannidis, especially during replications.
" In the biomedical sciences and elsewhere, scientists have only a superficial training in statistics and methodology ", adds John Ioannidis. [19659015] Too many studies focus on only a few individuals, making it impossible to generalize to an entire population, because the selected participants are unlikely to be representative.
Coffee and Red Wine
" The diet is one of the most appalling areas ", continues Professor Ioannidis, and not only because of conflicts of interest with the agri-food industry. Researchers often go in search of correlations in huge databases, without any starting hypothesis.
In addition, " measuring a diet is extremely difficult ," he says. How to quantify exactly what people eat?
Even when the method is good with a randomized study, where participants are randomly selected, the leaves a lot to be desired
A famous 2013 study on the benefits of the Mediterranean diet for heart disease had to be withdrawn in June by the most prestigious medical journal, the New England Journal of Medicine, because not all participants were randomly recruited; the results have been revised downwards
While in the flow of published studies every day?
John Ioannidis recommends asking the following questions: Is such a study isolated, or does it reinforce existing work? Is the sample small or large? Is this a randomized experiment? Who financed it? Are researchers transparent?
These precautions are fundamental in medicine where bad studies contribute to the adoption of treatments at best ineffective, and at worst harmful.
In their book " Ending Medical Reversal ", Vinayak Prasad and Adam Cifu describe terrifying examples of practices adopted on the basis of studies that were invalidated years later, such as stenting (mini prostheses) in an artery of the brain to reduce the risk of stroke. It was only after ten years that a rigorous study showed that the practice … actually increased the risk of stroke.
The solution involves the collective tightening of the criteria for all actors of research, not just journals: universities, public funding agencies, laboratories … But these institutions are all subject to competition.
" The system does not encourage people to go into the right direction ", says Ivan Oransky, co-founder of the Retraction Watch website, which covers withdrawals of scientific articles. " We want to develop a culture where we reward transparency ."
The problem also comes from the media which must, according to him, better explain to their readers the uncertainties inherent in scientific research, and withstanding sensationalism .
" The problem is the endless succession of studies on coffee, chocolate and red wine ", he complains. " We must stop ."
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