$n$個のデータ\[x_{1},x_{2},\cdots,x_{n}\]が正規分布$N(\mu,\sigma^{2})$に独立に従うとき,\[S/\sigma^{2}=\Sigma^{n}_{i=1}(x_{i}-\bar{x})^{2}/\sigma^{2}\]は自由度\[\phi=n-1\]の$\chi^{2}$分布に従う.
Mathematics is the language with which God has written the universe.