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## Variance and Standard Deviation

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**Variance and Standard Deviation**The most important measures of “spread” or dispersion**Sample Variance**The variance is the average squared deviation away from the mean. For a sample of size n, divide by n – 1. For a population, divide by n. Sample mean x**The standard deviation**The standard deviation is simply the square root of the variance. The variance must always be calculated before the standard deviation.**Population mean μ**σ and σ2 are pronounced “sigma” and “sigma squared”, respectively.**The coefficient of variation (CV)**The coefficient of variation standardizes the standard deviation by dividing by the mean.**The Empirical Rule*** This is actually a normal, continuous distribution, also known as a “bell curve”.**mode = median = mean**mode < median < mean mode > median > mean**The amount of skewness is measured using Pearson’s**coefficient of skewness (sk):