### PopulationStdDev (fld), PopulationStdDev (fld, condFld), PopulationStdDev (fld, condFld, cond), PopulationStdDev (x)

Basic and Crystal syntax.

##### Arguments

- fld is any valid database or formula field that can be evaluated by the function.
- condFld is a field used to group the values in fld by.
- cond is a String indicating the type of grouping for condFld. You only specify this argument when condFld is a Date, Time, DateTime or Boolean field.

  For more information on the valid strings for this argument, see Conditions for summary functions.

- x is an array of values that can be evaluated by the function being used.

##### Returns

Fractional Number

##### Action

Enables you to find the population standard deviation of a set of values in your report. For example:

- You can calculate the grand total population standard deviation for all values in a field. For information on this kind of summary, see SummaryFunction (fld).
- You can calculate the population standard deviation for all values within a group (for example, sales grouped by the state that they come from). For information on this kind of summary, see SummaryFunction (fld, condFld).
- You can calculate the population standard deviation for all values within a group in which grouping is controlled by changes in a date or Boolean field (for example, sales grouped by the month in which they were made). For information on this kind of summary, see SummaryFunction (fld, condFld, cond).
- If you specify a set of individual values, you can compute the population standard deviation of the values in the set. For information on this kind of summary, see Array summary functions (x).

##### Examples

The following examples are applicable to both Basic and Crystal syntax:

`PopulationStdDev({file.SCORES})`

Calculates the population standard deviation of all values in the Scores field for the entire report.

`PopulationStdDev({orders. AMOUNT}, {orders.CUSTOMER ID})`

Calculates the population standard deviation for the orders in each group of orders in the Amount field. The orders are separated into groups whenever the value in the Customer ID field changes.

`PopulationStdDev({file.RESULTS}, {file.DATE}, "daily")`

Calculates the variation for each group of laboratory test results in the Results field. The test results are separated into groups whenever the value in the Date field changes to a new day.

The following example is applicable to Crystal syntax:

`PopulationStdDev([{file.QTY1}, {file.QTY2}, {file.QTY3}, {file.QTY4}])`

Returns 3.57 where Qty1 = 2, Qty2 = 2, Qty3 = 10, and Qty4 = 8.

##### Comments

Population standard deviation is calculated using the following technique:

- It calculates the average (mean) value for the items in the population.
- It subtracts the average value from the value of each item.
- It squares the difference for each item.
- It adds the squared differences for all of the items in the population.
- It divides the sum by the number of items in the population (N). The result is the population variance. Compare this step to the StdDev (fld), StdDev (fld, condFld), StdDev (fld, condFld, cond), StdDev (x).
- It calculates the square root of the population variance to arrive at the population standard deviation.

Note: Using this function in a formula forces the formula to be evaluated at print time.

For more information on evaluation time considerations, see the Evaluation Time functions.

Seagate Software, Inc. http://www.seagatesoftware.com Please send comments to: techpubs@seagatesoftware.com