, Volume 43, Issue 1, pp 7-9
Date: 14 Aug 2013

Bayesian Advice for Gaydar-based Picking Up: Commentary on Lyons, Lynch, Brewer, and Bruno (2013)

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Consider the following: About 5 % of people are homosexual. Is it possible to detect from appearance if somebody is homosexual? This seems to be possible. In a recent study, participants were able to detect if somebody was homosexual better than chance. In this study, participants had to judge the sexual orientation of individuals based on 80 photographs of faces: 40 photographs depicted a homosexual person; the other 40 photographs depicted a heterosexual person. It turned out that 70 % of the homosexual persons were correctly identified. Of the heterosexual pictures, only 20 % were incorrectly classified as homosexual.

Now the question: Assume that all individuals can be as accurate in detecting sexual orientation as in this study. If one sees a randomly chosen individual in the street and judges the person to be homosexual, what is the chance (between 0 and 100 %) that the person is indeed homosexual?

You may be surprised that the correct answer is a quite low probability: 16 %. ...