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Thrasymachus comments on Why the tails come apart - Less Wrong

115 Post author: Thrasymachus 01 August 2014 10:41PM

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Comment author: Thrasymachus 02 August 2014 02:07:38AM 4 points [-]

There's also a related problem in that population substructures can give you multiple negatively correlated associations stacked beside each other in a positively correlated way (think of it like several diagonal lines going downwards to the right, parallel to each other), giving an 'ecological fallacy' when you switch between levels of analysis.

(A real-world case of this is religiosity and health. Internationally, countries which are less religious tend to be healthier, but often within first world countries, religion confers a survival benefit.)

Comment author: tjohnson314 09 June 2015 08:45:12PM 1 point [-]

Another example I've heard is SAT scores. At any given school, the math and verbal scores are negatively correlated, because schools tend to select people who have around the same total score. But overall, math and verbal scores are positively correlated.