Mercurial > octave
view scripts/statistics/tests/prop_test_2.m @ 3457:e031284eea27
[project @ 2000-01-19 08:49:56 by jwe]
author | jwe |
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date | Wed, 19 Jan 2000 08:50:14 +0000 |
parents | 434790acb067 |
children | 38c61cbf086c |
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## Copyright (C) 1996, 1997 Kurt Hornik ## ## This program is free software; you can redistribute it and/or modify ## it under the terms of the GNU General Public License as published by ## the Free Software Foundation; either version 2, or (at your option) ## any later version. ## ## This program is distributed in the hope that it will be useful, but ## WITHOUT ANY WARRANTY; without even the implied warranty of ## MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU ## General Public License for more details. ## ## You should have received a copy of the GNU General Public License ## along with this file. If not, write to the Free Software Foundation, ## 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA. ## -*- texinfo -*- ## @deftypefn {Function File} {[@var{pval}, @var{z}] =} prop_test_2 (@var{x1}, @var{n1}, @var{x2}, @var{n2}, @var{alt}) ## If @var{x1} and @var{n1} are the counts of successes and trials in ## one sample, and @var{x2} and @var{n2} those in a second one, test the ## null hypothesis that the success probabilities @var{p1} and @var{p2} ## are the same. Under the null, the test statistic @var{z} ## approximately follows a standard normal distribution. ## ## With the optional argument string @var{alt}, the alternative of ## interest can be selected. If @var{alt} is @code{"!="} or ## @code{"<>"}, the null is tested against the two-sided alternative ## @var{p1} != @var{p2}. If @var{alt} is @code{">"}, the one-sided ## alternative @var{p1} > @var{p2} is used. Similarly for @code{"<"}, ## the one-sided alternative @var{p1} < @var{p2} is used. ## The default is the two-sided case. ## ## The p-value of the test is returned in @var{pval}. ## ## If no output argument is given, the p-value of the test is displayed. ## @end deftypefn ## Author: KH <Kurt.Hornik@ci.tuwien.ac.at> ## Description: Compare two proportions function [pval, z] = prop_test_2 (x1, n1, x2, n2, alt) if ((nargin < 4) || (nargin > 5)) usage ("[pval, z] = prop_test_2 (x1, n1, x2, n2, alt)"); endif ## Could do sanity checking on x1, n1, x2, n2 here p1 = x1 / n1; p2 = x2 / n2; pc = (x1 + x2) / (n1 + n2); z = (p1 - p2) / sqrt (pc * (1 - pc) * (1/n1 + 1/n2)); cdf = stdnormal_cdf (z); if (nargin == 4) alt = "!="; endif if (! isstr (alt)) error ("prop_test_2: alt must be a string"); endif if (strcmp (alt, "!=") || strcmp (alt, "<>")) pval = 2 * min (cdf, 1 - cdf); elseif strcmp (alt, ">") pval = 1 - cdf; elseif strcmp (alt, "<") pval = cdf; else error ("prop_test_2: option %s not recognized", alt); endif if (nargout == 0) printf (" pval: %g\n", pval); endif endfunction