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Science: Many studies focus on a few individuals, making it impossible to generalize to a whole population (Paul Gilham / Getty Images / Getty Images)
A few years ago, two researchers selected the 50 most commonly used ingredients in a cookbook and badyzed how many of them had been badociated with cancer risk or benefit in several studies published in scientific journals.
The answer: 40 out of 50, a list that includes salt, flour, parsley and sugar. "All we eat is linked to cancer?", They make irreverent comments in their 2013 article.
Your question is related to a known but persistent problem in the research world: many studies use samples But the pressure on researchers, the competition between newspapers and the insatiable appetite of the media for studies that announce revolutions or major breakthroughs make these articles continue to be published.
Most of the articles published, even in serious journals, are weak, "AFP John Ioannidis, a professor of medicine at Stanford, who specializes in medical studies, told AFP. study
"because most of the published studies are false."
Since then, he says, only some progress has been made.
Some journals require that they provide their raw data and publish their protocol to This transparency prevents researchers from modifying their methods and data to find a result, no matter what, it also allows others to check or "replicate" them. study
When they are repeated, the experiments rarely lead to the same results: one-third of the 100 studies published in the three most prestigious psychology journals could be reproduced by researchers in an badysis published in 2015. [19659004] Medicine, epidemiology, clinical drug trials and nutritional studies do not work much better "
" In biomedical sciences and elsewhere, scientists are not trained enough in statistics and methodology, " he added.
Many studies focus on a few individuals, which makes them with the result that it is impossible to generalize to a total population, since selected participants are unlikely to be representative.
Coffee and Red Wine
"The diet is one of the most regrettable regions," says Ioannidis, not only because of conflicts of interest with the agri-food industry . Researchers often look for correlations in large databases, with no chance of getting started.
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 random study where participants are chosen at random, the execution sometimes leaves something 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 prestigious medical journal The New England Journal of Medicine, since the participants were not recruited in such a way random;
Ioannidis recommends asking the following questions: Is it an isolated study or does it strengthen existing work? Is the sample small or big? Is it a random experience? Who funded it?
In his book "Ending Medical Reversal", he writes: "To be able to do that, Vinayak Prasad and Adam Cifu cite terrifying examples of practices adopted on the basis of studies that were invalidated years later, like stent placement in an artery of the brain to reduce the risk of stroke.Ten years later, a rigorous study showed that the practice increased the risk of stroke.
The solution requires a collective adjustment of common criteria for research officers, not just journals: universities, public funding agencies, laboratories
"The system does not encourage people to go in the right direction", said AFP Ivan Oransky, a reporter co-founder of Retraction Watch, which covers withdrawals of scientific papers. "We want to develop a culture in which we reward transparency."
The Media o They also feel that they should be better able to explain to their readers the uncertainties inherent in scientific research and avoid sensationalism. The problem is the endless succession of studies on coffee, chocolate and red wine, "he complains. "We have to stop."
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