Probability and Statistics

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\frac{d}{dx} \sin x=?\, This article/section deals with mathematical concepts appropriate for a student in late high school or early university.

Variance is a measure in statistics of the dispersion of a set of values (represented as X). It is defined as

\sigma^2 = \operatorname{E}[(X-\operatorname{E}[X])^2] = \operatorname{E}[X^2] - (\operatorname{E}[X])^2

where the expected value of X is E(X).

The formula for variance must not be confused with the formula

S_{n}^2 =  {\sum_n(x - \bar x)^2 \over n - 1}

which is the formula for a point estimate of the true variance from a sample of size n. As such this estimator itself has a variance which, as the formula indicates, decreases as the sample size increases.

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