# Standard Deviation

### Statistics 101

<h3>What is it?</h3>

The standard deviation is a measure of dispersion of a group of values, calculated by taking the square root of the variance.

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<h3>What does it do?</h3>

The standard deviation (SD) is an estimate for the average distance to the mean, and is expressed in the same units as the original observations. Thus, it tells us how tightly data is clustered around the mean. In the bell-shaped normal distribution, each band has a width of one standard deviation. Therefore, a p-value of <0.05 is practically the same as an observation being at least 2 SD away from the null expectation.

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<h3>Useful to know</h3>

If the standard deviation is large compared to the mean, it indicates that the values are spread over a wider range, meaning that there is a high variety within the dataset, making it less reliable.