Σ ( α i − μ ) 2 n where μ is the mean α i is each number in the data set n is the number of points {\displaystyle {\begin{array}{lcl}{\sqrt {\frac {\Sigma (\alpha _{i}-\mu )^{2}}{n}}}\\\\{\mbox{where}}~\mu \ {\mbox{is the mean}}\\\alpha _{i}\ {\mbox{is each number in the data set}}\\n\ {\mbox{is the number of points}}\\\end{array}}}
