How do you write the Standard Deviation formula in MS SQL

Estimating population standard deviation from sample standard deviation
In the real world, finding the standard deviation of an entire population is unrealistic except in certain cases, such as standardized testing, where every member of a population is sampled. In most cases, the standard deviation is estimated by examining a random sample taken from the population. The most common measure used is the sample standard deviation, which is defined by

 See attached formula.


where  is the sample and  is the mean of the sample. The denominator N  1 is the number of degrees of freedom in the vector .

The reason for this definition is that s2 is an unbiased estimator for the variance Ã2 of the underlying population, if that variance exists and the sample values are drawn independently with replacement. However, s is not an unbiased estimator for the standard deviation Ã; it tends to underestimate the population standard deviation. Although an unbiased estimator for à is known when the random variable is normally distributed, the formula is complicated and amounts to a minor correction. Moreover, unbiasedness, in this sense of the word, is not always desirable; see bias of an estimator.

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