p values and the  standard   Hi Im curious about the origins of the  p value standard and didnt want to continue the discussion on the homeopathy talk page so I hope you dont mind a question here  I admittedly oversimplified my statement about  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 Im 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  Puddinhead