Statistical Significance

Statistical significance is a measure of how likely an observed result would be if there were really no effect at all, formalised by Ronald Fisher in his 1925 book Statistical Methods for Research Workers around the p-value and the conventional threshold of p less than 0.05. It became the standard test across experimental science for deciding whether a result is worth taking seriously. It is also one of the most criticised tools in modern statistics: a result below the threshold is not the same as a result that matters in practice, the 0.05 cutoff is an arbitrary convention Fisher himself did not intend as a rigid rule, and the American Statistical Association issued a formal 2016 statement warning against treating it as a substitute for judgment; this contested standing is a live thread in the reproducibility crisis entry below.