Why medical studies are often wrong

“One obvious problem is that studies vary in size and quality. Some are well-designed, others are not, yet most media reports give all of them the same status “” the medical variant of ‘astonomers say one thing, astrologers another, so let’s hear from both.’ Margins of error, low correlations, or very large ones that mask confounding variables seldom make it into the lede of news stories, whereas ‘X will cure you’ or ‘Y will kill you’ always seem to.

Another issue is that many health studies rely on self-reporting, which is notoriously unreliable. The average number of sex partners reported by heterosexual males, for example, is almost always considerably larger than the average number reported by heterosexual females. Certainly if these numbers, which should be equal, are so out of whack, it’s hard to put too much credence into sex surveys as a whole. Similar bias results if people are asked whether their incessant drinking of green tea has lessened their angina.”