Quote of the Day 17 December 2013 – Deviation

Pattern standard deviation

Pattern standard deviation (Photo credit: Community Eye Health)

“The value for which P=0.05, or 1 in 20, is 1.96 or nearly 2; it is convenient to take this point as a limit in judging whether a deviation ought to be considered significant or not. Deviations exceeding twice the standard deviation are thus formally regarded as significant. Using this criterion we should be led to follow up a false indication only once in 22 trials, even if the statistics were the only guide available. Small effects will still escape notice if the data are insufficiently numerous to bring them out, but no lowering of the standard of significance would meet this difficulty.”
Ronald A. FisherDesign Of Experiments

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