4.1.3.2.15 ConfidenceIntervalOfTotal

ConfidenceIntervalOfTotal function

Prototype:	function ConfidenceIntervalOfTotal (const NSample :integer; const VarianceOfTotal :extended; const Alpha :integer {5} ) : extended;
Description:	Calculates the width of alpha-confidence interval of variable with specified number of observations and variance
Syntax:	variable := ConfidenceIntervalOfTotal (NSample, VarianceOfTotal, Alpha);
	Part	Description
	variable	A variable declared as type of extended
	NSample	Number of observations in sample
	VarianceOfTotal	Sample variance of total
	Alpha	Confidence level

Return value:	Width of confidence interval
Note:	Calculations are based on the presumption of unknown population standard deviation, i.e. quantiles of Students distribution are used.

Example:

var
  tab : TTableWrapper;
  attributeName: string;
  nullAsZero: boolean;
  v, vt, c: extended;

begin
  tab:= Trees.table;
  attributeName:= 'DBH_mm';
  nullAsZero:= false;                  

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

  vt:= VarianceOfTotal(v, 4);

  c:= ConfidenceIntervalOfTotal(Trees.RecordCount, vt, 5);

  ShowMessage(FloatToStr(c));
end.