. this usage of 'three-sigma rule' entered common usage in the 2000s, e.g. Cited in Schaum's Outline of Business Statistics. McGraw Hill Professional. P. 359, and in Grafarend, Erik W. Linear and Nonlinear Models: Fixed Effects, Random Effects, and Mixed Models.
Walter de Gruyter. P. 553. See:. Wheeler, D. J.; Chambers, D. SPC Press. Czitrom, Veronica; Spagon, Patrick D.
P. 342. Pukelsheim, F. 'The Three Sigma Rule'. American Statistician. 48: 88–91.External links. ' by Balasubramanian Narasimhan. ' at WolframAlpha.
Standard deviation (σ) is the measure of spread of numbers from the mean value in a given set of data. Sample SD formula is S = √∑ (X - M) 2 / n - 1. Population SD formula is S = √∑ (X - M) 2 / n. Mean(M) can be calculated by adding the X values divide by the Number of values (N). Percent deviation measures the degree to which individual data points in a statistic deviate from the average measurement of that statistic. To calculate percent deviation, first determine the mean of the data and the average deviation of data points from that mean.