# StdDev

The **StdDev** function computes the standard deviation of a column or group. It measures the spread of a set of observations (numbers) around the mean and is calculated as the square root of the variance. A low standard deviation suggests data points are clustered near the mean, whereas a high standard deviation suggests data points are generally far from the mean.

Standard deviation is a useful measure of spread for symmetrical distributions with no outliers. It is expressed in the same units of measurement as the data and can help determine the statistical distribution of a dataset.

### Syntax

`StdDev(column)`

Function arguments:

* **column** (required) - The column of numbers to be measured.

The underlying formula is as follows:

```
√(x_i-x)^2/n-1
```

where `x_i` is the value of one observation, x is the mean value of all observations, and n is the number of observations (sample size). 

### Example

```
StdDev([x])
```

* Return the sample standard deviation of non-null records in the *x* column for each group *K*.

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