Worth reading: http://slatestarcodex.com/2016/03/16/non-shared-environment-doesnt-just-mean-schools-and-peers/ http://slatestarcodex.com/2016/03/16/non-shared-e

Worth reading: http://slatestarcodex.com/2016/03/16/non-shared-environment-doesnt-just-mean-schools-and-peers/ http://slatestarcodex.com/2016/03/16/non-shared-environment-... He makes a lot of points here, but the most important IMO is that many measurements are noisy, and the correlation between X and Y+noise is less than the correlation between X and Y.