Standard deviation is the positive square root of variance. Standard deviation measures dispersion (as does variance), but it is measured in the same units as the variable.
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Summary
ere σ 2 (X) stands for the variance of X. Variance is a measure of dispersion about the mean. Increasing variance indicates increasing dispersion. Variance is measured in squared units of the original variable. <span>Standard deviation is the positive square root of variance. Standard deviation measures dispersion (as does variance), but it is measured in the same units as the variable. Covariance is a measure of the co-movement between random variables. The covariance between two random variables R i and R j is the expected value of t