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 p values and the 0.05 standard 

Hi, I'm curious about the origins of the 0.05 p -value standard and didn't want to continue the discussion on the homeopathy talk page, so I hope you don't mind a question here.  I admittedly oversimplified my statement about 0.05 being arbitrary, mainly in an effort to save space and not overexert myself in addressing another editor.  Clearly, ""arbitrary"" was not the best word, but what I'm curious about is the origins of two standard deviations being established as the cut off for significance.  Is there any inherent reason why two SDs are significant, or is it simply a convenient attribute of any distribution which can be used to define outlying data points?  Thanks for the clarification. - Puddin'head64.58.20.99  "