1 ## Copyright (C) 1996-2012 Kurt Hornik
3 ## This file is part of Octave.
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6 ## under the terms of the GNU General Public License as published by
7 ## the Free Software Foundation; either version 3 of the License, or (at
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13 ## General Public License for more details.
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20 ## @deftypefn {Function File} {[@var{pval}, @var{z}] =} prop_test_2 (@var{x1}, @var{n1}, @var{x2}, @var{n2}, @var{alt})
21 ## If @var{x1} and @var{n1} are the counts of successes and trials in
22 ## one sample, and @var{x2} and @var{n2} those in a second one, test the
23 ## null hypothesis that the success probabilities @var{p1} and @var{p2}
24 ## are the same. Under the null, the test statistic @var{z}
25 ## approximately follows a standard normal distribution.
27 ## With the optional argument string @var{alt}, the alternative of
28 ## interest can be selected. If @var{alt} is @code{"!="} or
29 ## @code{"<>"}, the null is tested against the two-sided alternative
30 ## @var{p1} != @var{p2}. If @var{alt} is @code{">"}, the one-sided
31 ## alternative @var{p1} > @var{p2} is used. Similarly for @code{"<"},
32 ## the one-sided alternative @var{p1} < @var{p2} is used.
33 ## The default is the two-sided case.
35 ## The p-value of the test is returned in @var{pval}.
37 ## If no output argument is given, the p-value of the test is displayed.
40 ## Author: KH <Kurt.Hornik@wu-wien.ac.at>
41 ## Description: Compare two proportions
43 function [pval, z] = prop_test_2 (x1, n1, x2, n2, alt)
45 if ((nargin < 4) || (nargin > 5))
49 ## Could do sanity checking on x1, n1, x2, n2 here
53 pc = (x1 + x2) / (n1 + n2);
55 z = (p1 - p2) / sqrt (pc * (1 - pc) * (1/n1 + 1/n2));
57 cdf = stdnormal_cdf (z);
64 error ("prop_test_2: ALT must be a string");
66 if (strcmp (alt, "!=") || strcmp (alt, "<>"))
67 pval = 2 * min (cdf, 1 - cdf);
68 elseif strcmp (alt, ">")
70 elseif strcmp (alt, "<")
73 error ("prop_test_2: option %s not recognized", alt);
77 printf (" pval: %g\n", pval);