StDev DataWindow expression function

Description

Calculates an estimate of the standard deviation for the specified
column. Standard deviation is a measurement of how widely values
vary from average.

Syntax

<span>StDev</span> ( <span>column</span> { FOR <span>range</span> { DISTINCT { <span>expres1</span> {, <span>expres2</span> {, ... } } } } } )

1	<span>StDev</span> ( <span>column</span> { FOR <span>range</span> { DISTINCT { <span>expres1</span> {, <span>expres2</span> {, ... } } } } } )

Argument	Description
column	The column for which you want an estimate for the standard deviation of the values in the rows. Column can be the column name or the column number preceded by a pound sign (#). Column can also be an expression that includes a reference to the column. The datatype of column must be numeric.
FOR range (optional)	The data to be included in the estimate of the standard deviation. For most presentation styles, values for range are: ALL – (Default) The estimate of the standard deviation for all values in column. GROUP n – The estimate of the standard deviation for values in column in the specified group. Specify the keyword GROUP followed by the group number: for example, GROUP 1. PAGE – The estimate of the standard deviation for the values in column on a page. For Crosstabs, specify CROSSTAB for range to indicate the standard deviation for all values in column in the crosstab. For Graph objects specify GRAPH and for OLE objects specify OBJECT to indicate the standard deviation for values in column in the range specified for the Rows option.
DISTINCT (optional)	Causes StDev to consider only the distinct values in column when determining the standard deviation. For a value of column, the first row found with the value is used and other rows that have the same value are ignored.
expresn (optional)	One or more expressions that you want to evaluate to determine distinct rows. Expresn can be the name of a column, a function, or an expression.

Return Values

Double. Returns an estimate of the standard deviation for column.

Usage

If you specify range, StDev returns
an estimate for the standard deviation of column within range.
If you specify DISTINCT, StDev returns an estimate
of the standard deviation for the distinct values in column,
or if you specify expresn, the estimate of
the standard deviation of the rows in column where
the value of expresn is distinct.

For graphs and OLE objects, you do not select the range when
you call the function. The range has already been determined by
the Rows setting on the Data tab page (the Range property), and
the aggregation function uses that range. Settings for Rows include
the following:

For the Graph or OLE
presentation style, Rows is always All.
For Graph controls, Rows can be All, Page, or Group.
For OLE controls, Rows can be All, Current Row,
Page, or Group. The available choices depend on the layer the control
occupies.

Estimating or calculating actual standard
deviation

StDev assumes that the values in column are
a sample of the values in the rows in the column in the database
table. If you selected all the rows in the column in the DataWindow object’s SELECT statement,
use StDevP to compute the standard deviation
of the population.

Not in validation rules or filter expressions

You cannot use this or other aggregate functions in validation
rules or filter expressions.

Using an aggregate function cancels the effect of setting
Retrieve Rows As Needed in the painter. To do the aggregation, a DataWindow object always retrieves
all rows.

Examples

These examples all assume that the SELECT statement
did not retrieve all the rows in the database table. StDev is
intended to work with a subset of rows, which is a sample of the
full set of data.

This expression returns an estimate for standard deviation
of the values in the column named salary:

<span>StDev</span>(salary)

1	<span>StDev</span>(salary)

This expression returns an estimate for standard
deviation of the values in the column named salary in group 1:

<span>StDev</span>(salary for group 1)

1	<span>StDev</span>(salary for group 1)

This expression returns an estimate for standard
deviation of the values in column 4 on the page:

<span>StDev</span>(#4 for page)

1	<span>StDev</span>(#4 for page)

This expression entered in the Value box on the Data
tab page in the graph’s property sheet returns an estimate
for standard deviation of the values in the qty_used column
in the graph:

<span>StDev</span>(qty_used for graph)

1	<span>StDev</span>(qty_used for graph)

This expression for a computed field in a crosstab
returns the estimate for standard deviation of the values in the
qty_ordered column in the crosstab:

<span>StDev</span>(qty_ordered for crosstab)

1	<span>StDev</span>(qty_ordered for crosstab)

Assuming a DataWindow object displays the order number,
amount, and line items for each order, this computed field returns
the estimated standard deviation of the order amount for the distinct
order numbers:

<span>StDev</span>(order_amt for all DISTINCT order_nbr)

1	<span>StDev</span>(order_amt for all DISTINCT order_nbr)

StDev – PB Docs 126