Why 0.05? because 1 in 20~22: two standard deviations. so if your distribution isn't normal Gaussian you don't even have tradition on your side, (or perhaps 1

Why 0.05? because 1 in 20~22: two standard deviations. so if your distribution isn't normal Gaussian you don't even have tradition on your side, (or perhaps 1 in 20 doesn't fit your risk model for say, testing pharmaceuticals?) http://www.jerrydallal.com/lhsp/p05.htm http://www.jerrydallal.com/lhsp/p05.htm "Still, why should the value 0.05 be adopted as the universally accepted value for statistical significance? ... It was Fisher who suggested giving 0.05 its special status... The value for which P=0.05, or 1 in 20, is 1.96 or nearly 2 ...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"