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// Scilab ( http://www.scilab.org/ ) - This file is part of Scilab
// Copyright (C) 2000 - INRIA - Carlos Klimann
//
// This file must be used under the terms of the CeCILL.
// This source file is licensed as described in the file COPYING, which
// you should have received as part of this distribution. The terms
// are also available at
// http://www.cecill.info/licences/Licence_CeCILL_V2.1-en.txt
//
function [dif]=nand2mean(sample1,sample2,conf)
//
//This function computes an estimate (dif(1)) for the
//difference of the means of two independent samples (arrays
//sample1 and sample2) and gives the half amplitude of the
//range of variability of dif with an indicated confidence
//level (dif(2)). The choice of the normal or t fonctions as
//the probability fonction depends on the sizes of sample1
//and sample2. We suppose that the underlying variances of
//both populations are equal. NAN values are not counted.
//
//In absence of the confidence parameter a confidence level
//of 95% is assumed.
//
//References: Wonacott, T.H. & Wonacott, R.J.; Introductory
//Statistics, J.Wiley & Sons, 1990.
//
//
[lhs,rhs]=argn(0)
if rhs<2|rhs>3 then
error(msprintf(gettext("%s: Wrong number of input arguments: %d to %d expected.\n"),"nand2mean",2,3)),
elseif rhs==2 then
conf=.975
end
if (sample1==[]|sample2==[]) then
dif=%nan
return,
end
isn1=isnan(sample1)
isn2=isnan(sample2)
sample1(isn1)=0
sample2(isn2)=0
n1=sum(bool2s(~isn1))
n2=sum(bool2s(~isn2))
mean1=sum(sample1)/n1
mean2=sum(sample2)/n2
svarp=sqrt((sum((sample1(~isn1)-mean1).^2)+sum((sample2(~isn2) ..
-mean2).^2))/(n1+n2-2))
dif(1)=mean1-mean2
if (n1+n2-2)>100 then
dif(2)=cdfnor("X",0,1,conf,1-conf)*svarp*sqrt((1/n1)+(1/n2))
else
dif(2)=cdft("T",n1+n2-2,conf,(1-conf))*svarp*sqrt((1/n1)+(1/n2))
end
endfunction
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