# StandardDeviation

Checks the standard deviation of all of the values in a column against a given expression.

**Syntax**

`StandardDeviation`

`<COL_NAME>`

`<EXPRESSION>`

**COL_NAME**– The name of the column that you want to evaluate the data quality rule against.**Supported column types**: Byte, Decimal, Double, Float, Integer, Long, Short**EXPRESSION**– An expression to run against the rule type response in order to produce a Boolean value. For more information, see Expressions.

**Example: Standard deviation**

The following example rule checks whether the standard deviation of the values in a
column named `colA`

is less than a specified value.

`StandardDeviation "Star_Rating" < 1.5 StandardDeviation "Salary" < 3500 where "Customer_ID < 10"`

**Sample dynamic rules**

`StandardDeviation "colA" > avg(last(10) + 0.1`

`StandardDeviation "colA" between min(last(10)) - 1 and max(last(10)) + 1`

**Null behavior**

The `StandardDeviation`

rule will ignore rows with `NULL`

values in the calculation of
standard deviation. For example:

`+---+-----------+-----------+ |id |units1 |units2 | +---+-----------+-----------+ |100|0 |0 | |101|null |0 | |102|20 |20 | |103|null |0 | |104|40 |40 | +---+-----------+-----------+`

The standard deviation of column `units1`

will not consider rows 101 and 103 and result to 16.33.
The standard deviation for column `units2`

will result in 16.