# Stdev (PQL)

Returns the sample standard deviation across elements in the specified list.

- Returned Output: Numeric
- Library: PQL \ Semantic \ Statistical
- Version: 2018.00.000
- Compatibility: Pyramid Query Language (PQL) data sources

#### Syntax

* Click on the function's arguments above for more details on the input values.

##### Comments

- There are 2 variants of the function: one for sample and one for the population ("P").
- List parameter should be a list or set of elements from an existing hierarchy in the model.
- The data point or tuple is optional, and describes the values used to generate the standard deviation . If not supplied, the default measure or the query context will determine this value instead.
- For details on how to employ and use this function see the semantic calculation overview.

##### Different Function types

- This function is like the MDX sample standard deviation function; it calculates the standard deviation across a list of elements in a hierarchy or attribute.
- To use a simple standard deviation mathematical operation on a list of numbers, use the Common library function.

#### Examples

This example returns the sample standard deviation (sample math) of expenses across the product category in the product table/ dimension, using the sample demo model:

StDev( {AllMembers([products].[Product Category])}, ([measures].[data Expenses]) )

Below, using the sample data of the 4 product categories we can use the above formula to calculate the sample standard deviation. Looking at the list below, the standard deviation value for expenses is 4,650,938: