4.1.3.2.9 VarianceOfMean

VarianceOfMean function

Prototype:	function VarianceOfMean (TableOrLayer :TObjectWrapper; const AttributeName :string; const NullAsZero :boolean; const NSample :integer; const NPopulation :extended) : extended;
Description:	Calculates variance of mean of a specific attribute
Syntax:	variable := VarianceOfMean (tab, AttributeName, NullAsZero, NSample, NPopulation);
	Part	Description
	variable	A variable declared as type of extended
	tab	Table containing source variables
	AttributeName	Attribute of source table containing data to enter calculations
	NullAsZero	Boolean expression defining whether to exclude null (false) entries or replace nulls with zeros (true)
	NSample	Number of observations in a sample
	NPopulation	Number of observations in a population

Return value:	Variance of mean

Example:

Task:

Calculate variance of mean of DBH.

Data stored in the database.

Script:

var

tab : TTableWrapper;

attributeName: string;

nullAsZero: boolean;

v: extended;

begin

tab:= Trees.table;

attributeName:= 'DBH_mm';

nullAsZero:= false; // dont want calculate with a null value

v:= VarianceOfMean(tab, attributeName, nullAsZero, Trees.RecordCount, 20);

ShowMessage(FloatToStr(v));

end.

Output in Field-Map Data Collector:

variance of mean of DBH