A group at ETH Zurich did this experiment in a rather elaborate way some years back [1]. They sent the same guy, who had only one very minor dental problem, to

A group at ETH Zurich did this experiment in a rather elaborate way some years back [1]. They sent the same guy, who had only one very minor dental problem, to 180 (!) dentists. About 25% of them incorrectly found cavities that they said had to be taken care of, some up to 6, and some in varying teeth. As an interesting extra they dressed him up in high and low socioeconomic status clothes (jeans, t-shirt and backpack vs. suit with Rolex and car keys) and found the "student" was 'overtreated' more than the business man. The assumption was that richer patients are more likely to get a second opinion, and thus the dentists didn't make up problems. [1] https://papers.ssrn.com/sol3/papers.cfm?abstract_id=3036573 https://papers.ssrn.com/sol3/papers.cfm?abstract_id=3036573