Andrew Gelman has a great blot post on this: http://www.stat.columbia.edu/~cook/movabletype/archives/2010/12/the_truth_wears.html http://www.stat.columbia.edu/

Andrew Gelman has a great blot post on this: http://www.stat.columbia.edu/~cook/movabletype/archives/2010/12/the_truth_wears.html http://www.stat.columbia.edu/~cook/movabletype/archives/2010... In a nutshell, the problem arises from trying to estimate small effects and then screening results on statistical significance.