1. standard deviation SD A measure of the range of values in a set of numbers. Standard deviation is a statistic used as a measure of the dispersion or variation in a distribution, equal to the square root of the arithmetic mean of the squares of the deviations from the arithmetic mean. The standard deviation of a random variable or list of numbers the lowercase greek sigma is the square of the variance. The standard deviation of the list x1, x2, x3. . . xn is given by the formula: sigma = sqrtx1-avgx^2 + x1-avgx^2 + . . . + xnavgx^2/n The formula is used when all of the values in the population are known. If the values x1. . . xn are a random sample chosen from the population, then the sample Standard Deviation is calculated with same formula, except that n-1 is used as the denominator. [dictionary. com http://dictionary. com/]. ["Barrons Dictionary of Mathematical Terms, second edition"]. 2. the square root of the variance
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