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Sander Greenland, professor emeritus of epidemiology at the UCLA Fielding School of Public Health, was quoted in a Bloomberg opinion piece about a recent federal court case in which a jury decided that a popular weed killer was a substantial factor in causing someone to contract non-Hodgkins lymphoma.
Scientists can’t, for the most part, prove that a given product caused a particular person to get cancer — not the way you can prove, say, that a car with faulty brakes caused a fatal crash. And so when a federal jury in San Francisco District Court decided that the weed killer Roundup was a “substantial factor” in causing someone to get a type of cancer called non-Hodgkins lymphoma, they didn’t actually have proof for the individual case. What they had was evidence that the product was a probable factor in the man’s cancer, based on studies that follow large populations.
Of course science should be the deciding factor in such cases, but there’s no sense in implying that scientists can do the impossible. What scientists and society at large have come to agree upon is that it’s reasonable to award people compensation if it’s more likely than not that they would have avoided the cancer if they’d been able to avoid the product in question. This latest verdict, announced yesterday, is the second in favor of a plaintiff who got cancer after using Roundup, made by Monsanto, which was recently acquired by Bayer. In the first case, the plaintiff was awarded $80 million.
Why can’t scientists prove individual cancer cases? Cancer epidemiologist Richard Stevens of the University of Connecticut explains using a seemingly straightforward example: cigarettes. There’s abundant evidence that they cause lung cancer. But some nonsmokers get lung cancer, and many smokers never do. This is because there are other factors at work in the determination of who gets cancer, including, some say, random copying errors in DNA.