Standard_Deviation ( Field ; MaxLoopCount ; StartIndex ; StdDeviation ; ArithMeanValue )

Calculate the standard deviation of a set of numbers.

Average rating: 4.1 (39 votes) Log in to vote

Kevin Woods
KWoods
http://www.RivieraCouches.co.uk

Sample input:

Standard_Deviation ( Table1::NumberField ; Get( FoundCount ) ; 1 ; 0 ; Arithmetic_Mean ( Table1::NumberField ; Get( FoundCount ) ; 1 ; 0 ) ) ;

Sample output:

1.5

Function definition: (Copy & paste into FileMaker's Edit Custom Function window)

/*
Standard_Deviation function

Author


Based on Standard Deviation - Formula 1 by Richard Bowles 'http://richardbowles.tripod.com/maths/normdist/calc_sd1.htm'

Format
Standard_Deviation( Field ; MaxLoopCount ; StartIndex ; StdDeviation ; ArithMeanValue ) ; 

Parameters
Field                    - The field containing the values to be calculated.
MaxLoopCount   - The maximum number of records to process ie. (Get(FoundCount)).
StartIndex          - Row index to start processing at. Normally 1.
StdDeviation       - Used to store the sum the of the field values. 
ArithMeanValue  - The Standard Deviation value of the Found Set.

Data type returned
Number

Description
Calculates the standard deviation of a set of numbers, by recursively calling this function for each row in a Found Set. 
Use the Arithmetic_Mean function to calculate the ArithMeanValue.

Example:   Standard_Deviation ( Table1::NumberField ; Get( FoundCount ) ; 1 ; 0 ; Arithmetic_Mean ( Table1::NumberField ; Get( FoundCount ) ; 1 ; 0 ) ) ; 

August 24, 2010
*/

Case ( MaxLoopCount > 0 ; 

Let ( [


Data =  GetNthRecord ( Field ; StartIndex ) ; 
SumValue = StdDeviation ; 
MeanValue =  Data -  ArithMeanValue ;
Value = MeanValue * MeanValue ;

Output = SumValue + Value ] ;

Case ( MaxLoopCount = StartIndex ; Sqrt ( Output / MaxLoopCount) ; Standard_Deviation ( Field ; MaxLoopCount ; StartIndex + 1 ; Output ; ArithMeanValue ) )
) )

Calculates the standard deviation of a set of numbers, by recursively calling this function for each row in a Found Set.
Use the Arithmetic_Mean function to calculate the ArithMeanValue.

Comments

		comment, VR Aug 28, 2010
How is this and the Arithmetic_Mean function preferable to using a summary field defined as Standard Deviation or Average - or the corresponding Stdev() and Average() aggregate functions?

Note: these functions are not guaranteed or supported by BrianDunning.com. Please contact the individual developer with any questions or problems.

Standard_Deviation ( Field ; MaxLoopCount ; StartIndex ; StdDeviation ; ArithMeanValue )

Comments

Support this website.

Support this website.