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
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StDev ( column { FOR range { DISTINCT { expres1 {, expres2 {, ... } } } } } ) |
|
Argument |
Description |
|---|---|
|
column |
The column for which you want an estimate for the |
|
FOR range (optional) |
The data to be included in the estimate of the
For Crosstabs, specify CROSSTAB for For Graph objects specify GRAPH and |
|
DISTINCT (optional) |
Causes StDev to consider only the distinct values in |
|
expresn (optional) |
One or more expressions that you want to evaluate to |
Return value
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:
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1 |
StDev(salary) |
This expression returns an estimate for standard deviation of the
values in the column named salary in group 1:
|
1 |
StDev(salary for group 1) |
This expression returns an estimate for standard deviation of the
values in column 4 on the page:
|
1 |
StDev(#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:
|
1 |
StDev(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:
|
1 |
StDev(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:
|
1 |
StDev(order_amt for all DISTINCT order_nbr) |
See also