# Standard Deviation

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Standard Deviation is a measure of how spread out numbers are. 
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It is the square root of the [Variance](https://ai.nuhil.net/statistics/variance). It is often more convenient than the variance because it has the same unit as the data points.

**Population Standard Deviation**, $$\sigma=\sqrt{\frac{1}{n}}\sum\_i^n(x\_{i}-\mu)^2$$ 

**Sample Standard Deviation**, $$\sigma=\sqrt{\frac{1}{1-n}}\sum\_i^n(x\_{i}-\overline{x})^2$$