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Three hundred thirty-five published articles from six medical journals that contained "negative" results were examined to determine the probability of detecting "small," "medium," and "large" therapeutic improvements. The mean probability of detecting a small effect size was.138; for a medium effect size, the probability was.387; and for a large effect size, it was.614. (Arch Intern Med1981;141-1307-1310)
James Reed (Tue,) studied this question.