https://astralcodexten.substack.com/p/selection-bias-is-a-fact-of-life

Sometimes people do amateur research through online surveys. Then they find interesting things. Then their commenters say it doesn’t count, because “selection bias!” This has been happening to Aella for years, but people try it sometimes on me too.

I think these people are operating off some model where amateur surveys necessarily have selection bias, because they only capture the survey-maker’s Twitter followers, or blog readers, or some other weird highly-selected snapshot of the Internet-using public. But real studies by professional scientists don’t have selection bias, because . . . sorry, I don’t know how their model would end this sentence.

The real studies by professional scientists usually use Psych 101 students at the professional scientists’ university. Or sometimes they will put up a flyer on a bulletin board in town, saying “Earn $10 By Participating In A Study!” in which case their population will be selected for people who want $10 (poor people, bored people, etc). Sometimes the scientists will get really into cross-cultural research, and retest their hypothesis on various primitive tribes - in which case their population will be selected for the primitive tribes that don’t murder scientists who try to study them. As far as I know, nobody in history has ever done a psychology study on a truly representative sample of the world population.

This is fine. Why?