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1 ## Copyright (C) 1996, 1997, 1998, 2000, 2002, 2005, 2006, 2007 |
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2 ## Kurt Hornik |
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3 ## |
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4 ## This file is part of Octave. |
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5 ## |
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6 ## Octave is free software; you can redistribute it and/or modify it |
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7 ## under the terms of the GNU General Public License as published by |
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8 ## the Free Software Foundation; either version 3 of the License, or (at |
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9 ## your option) any later version. |
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10 ## |
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11 ## Octave is distributed in the hope that it will be useful, but |
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12 ## WITHOUT ANY WARRANTY; without even the implied warranty of |
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13 ## MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU |
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14 ## General Public License for more details. |
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15 ## |
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16 ## You should have received a copy of the GNU General Public License |
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17 ## along with Octave; see the file COPYING. If not, see |
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18 ## <http://www.gnu.org/licenses/>. |
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19 |
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20 ## -*- texinfo -*- |
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21 ## @deftypefn {Function File} {[@var{pval}, @var{z}] =} prop_test_2 (@var{x1}, @var{n1}, @var{x2}, @var{n2}, @var{alt}) |
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22 ## If @var{x1} and @var{n1} are the counts of successes and trials in |
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23 ## one sample, and @var{x2} and @var{n2} those in a second one, test the |
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24 ## null hypothesis that the success probabilities @var{p1} and @var{p2} |
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25 ## are the same. Under the null, the test statistic @var{z} |
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26 ## approximately follows a standard normal distribution. |
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27 ## |
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28 ## With the optional argument string @var{alt}, the alternative of |
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29 ## interest can be selected. If @var{alt} is @code{"!="} or |
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30 ## @code{"<>"}, the null is tested against the two-sided alternative |
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31 ## @var{p1} != @var{p2}. If @var{alt} is @code{">"}, the one-sided |
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32 ## alternative @var{p1} > @var{p2} is used. Similarly for @code{"<"}, |
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33 ## the one-sided alternative @var{p1} < @var{p2} is used. |
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34 ## The default is the two-sided case. |
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35 ## |
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36 ## The p-value of the test is returned in @var{pval}. |
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37 ## |
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38 ## If no output argument is given, the p-value of the test is displayed. |
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39 ## @end deftypefn |
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40 |
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41 ## Author: KH <Kurt.Hornik@wu-wien.ac.at> |
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42 ## Description: Compare two proportions |
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43 |
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44 function [pval, z] = prop_test_2 (x1, n1, x2, n2, alt) |
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45 |
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46 if ((nargin < 4) || (nargin > 5)) |
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47 print_usage (); |
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48 endif |
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49 |
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50 ## Could do sanity checking on x1, n1, x2, n2 here |
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51 |
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52 p1 = x1 / n1; |
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53 p2 = x2 / n2; |
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54 pc = (x1 + x2) / (n1 + n2); |
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55 |
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56 z = (p1 - p2) / sqrt (pc * (1 - pc) * (1/n1 + 1/n2)); |
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57 |
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58 cdf = stdnormal_cdf (z); |
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59 |
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60 if (nargin == 4) |
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61 alt = "!="; |
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62 endif |
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63 |
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64 if (! ischar (alt)) |
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65 error ("prop_test_2: alt must be a string"); |
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66 endif |
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67 if (strcmp (alt, "!=") || strcmp (alt, "<>")) |
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68 pval = 2 * min (cdf, 1 - cdf); |
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69 elseif strcmp (alt, ">") |
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70 pval = 1 - cdf; |
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71 elseif strcmp (alt, "<") |
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72 pval = cdf; |
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73 else |
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74 error ("prop_test_2: option %s not recognized", alt); |
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75 endif |
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76 |
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77 if (nargout == 0) |
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78 printf (" pval: %g\n", pval); |
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79 endif |
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80 |
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81 endfunction |
