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There's a simpler mathematical explanation. It's called Regression Towards the Mean: https://en.wikipedia.org/wiki/Regression_toward_the_mean https://en.wikipe

• thaumasiotes 8y ago
  That is not actually an explanation; you can only apply regression to the mean if you know what the mean is. The explanation I give correctly predicts that replicated experiments will see their effect sizes decline. Saying "regression to the mean" does not. (It is quite possible to interpret this as regression driven by the p-value threshold, but if you do that, you're relying on the explanation I gave.)
  • overeater 8y ago
    That's not true. If I take the top 5 students based on performance in a test, and put them in a group. They will likely do worse the second time around. No need to know the mean.