If I were to look at you, and say, in a serious tone of voice, “The cause of car accidents is cars”, you’d think I’m nuts. It’s not a useful statement. Yet many medical and science experts — including the people who award the Nobel Prize in Physiology or Medicine — believe it is helpful to say “the cause of ulcers is bacteria”. The two statements are similar because only a small percentage of cars get in accidents and only a small percentage of people infected with H. pylori, the bacterium that supposedly “causes ulcers”, get ulcers. A helpful investigation of what causes ulcers would figure out the crucial difference(s) between those infected with H. pylori who don’t get ulcers (almost all) and those who do (very few).
I recently encountered the “the cause of ulcers is bacteria” twice in one day. Once in a book review by John Timpane:
Barry Marshall, who discovered what causes stomach ulcers, played fast, loose, and messy with his methods and data. He was right, and got the right answer, and now we know.
(Timpane is right about the “fast, loose, and messy” part. Marshall ingested a large number of H. pylori. He failed get an ulcer — and claimed the outcome supported his view that H. pylori causes ulcers.) And once in The New Yorker, in a long article about the benefits of microbes, especially H. pylori, by Michael Specter:
In 1982, to the astonishment of the medical world, two scientists, Barry Marshall and J. Robin Warren, discovered that H. pylori is the principal cause of gastritis and peptic ulcers.
Should I expect science journalists to understand causality? Maybe not. But it is interesting that the people who award the Nobel Prize in Medicine and “the medical world” do not understand it.