[Octave-bug-tracker] [bug #58838] Statistics package - chisquare_test_homogeneity result does not equal equivalent chisquare_test_independence

[Tasos Papastylianou]

URL:
  <https://savannah.gnu.org/bugs/?58838>

                 Summary: Statistics package - chisquare_test_homogeneity
result does not equal equivalent chisquare_test_independence
                 Project: GNU Octave
            Submitted by: tpapastylianou
            Submitted on: Mon 27 Jul 2020 05:09:56 PM UTC
                Category: Octave Forge Package
                Severity: 3 - Normal
                Priority: 5 - Normal
              Item Group: None
                  Status: None
             Assigned to: None
         Originator Name: Tasos Papastylianou
        Originator Email: 
             Open/Closed: Open
                 Release: 5.2.0
         Discussion Lock: Any
        Operating System: Any

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Details:

Prompted by this question: https://stackoverflow.com/a/63119920/4183191

If my understanding of how chisquare_test_homogeneity is supposed to work (as
described in that stackoverflow post) is correct, then the following two
should have been equivalent, but in fact the resulting p-value is different. 


x = [ones(1,10), zeros(1,10)];
y = [ones(1,5 ), zeros(1,15)];
chisquare_test_homogeneity (x, y, 0.5)
% pval: 0.31731

chisquare_test_independence ( [10, 10; 15, 5] )
% pval: 0.10247


While the code involved in the m-file is fairly short and simple, the
documentation of this function is paltry. Also the implementation seems to
rely on some sort of 'cumulative' version of the chi square, which I have not
seen before. Is there a reference for this?




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