Variance
The variance of a data set is a measure of how "spread out" the data points are in general.
Formula
Population
For a dataset 
with mean 
the formula for variance if 
is a population is ![\[V = \frac{1}{n}\sum_{i=1}^n (x_i - \overline{x})^2.\]](http://latex.artofproblemsolving.com/b/4/c/b4c75e6bef818578a9483a944580f344bcf1cb09.png)
Additionally, 
where 
is the population standard deviation.
Sample
Because of Bessel's correction the variance if is a sample is calculated according to the slightly different formula ![\[V = \frac{1}{n-1}\sum_{i=1}^n (x_i - \overline{x})^2.\]](http://latex.artofproblemsolving.com/a/4/d/a4d2cd80aafdc103d50eb4f69dbf4ece5edd742a.png)
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