# stddev()

Returns the standard deviation of the values in a field. Accepts measure fields (but not expressions) as input.

## Example - Look at Variability in Amount

Use `stddev()` to get a feel for the amount of spread, or dispersion, in the size of your deals.

```nolang
q = load "DTCOpps";
q = group q by all;
q = foreach q generate stddev('Amount') as 'stddev_Amount';
```

## Should I Use stddev() or stddevp()?

Use `stddev()` when the values in your field are a partial sample of the entire set of values (that is, a partial sampling of the whole population). Use `stddevp()` when your field contains the complete set of values (that is, the entire population of values).

**See Also**

- [stddevp()](/docs/analytics/bi-dev-guide-saql/guide/bi-saql-fn-agg-stdevp.md)