While most ELS Blog readers understand traditional significance ("p") levels, few understand how (or why) "0.05" emerged as the standard for statistical significance. In The Adoption of Significance Tests by the Scientific Community: An Empirical Analysis, David A. Gully (Columbia--Engineering) discusses the adoption of the 0.05 standard. A excerpted abstract follows:
"This paper adds to the literature by determining the timing and level of acceptance of common tests of statistical inference. Using the archives of the Royal Society, we examined 574 research studies published between 1926 and 1997, by which point adoption was virtually complete... We detect the presence of several influences on the rate of adoption, which may include prior custom, the nature of empirical research topics being reported, the increasing ease of computer processing, and possibly journal editorial policies. We find that confidence/significance testing has been adopted by a majority of the scientific community for over 50 years; the customary reliance on 95 percent confidence (five percent significance) is upheld by the data; and that confidence intervals and critical significance levels are both widely reported and often together in recent decades."