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Re: Chi2 test

From: Nicholas Jankowski
Subject: Re: Chi2 test
Date: Wed, 13 Feb 2019 17:35:02 -0500

(fyi, the convention is to trim text and bottompost on this help-list)

On Wed, Feb 13, 2019 at 4:58 PM Javier Garcia Falaguera <address@hidden> wrote:
Hi Nicholas,

Thanks for the support.

The expected result is something like:

pval_mu = something aprox to 0, but no 0.0
chisq_mu = a positive value
df_mu = 21 (not a value of interest);

running the same data, I get the following:

 pval_mu =  NaN
chisq_mu =  NaN
df_mu =  21

looking at the function (you can type  'edit chisquare_test_homogeneity' to open m-file functions and step through the code)

df is just the length of c, so df = 21

chisq gives NaN because the values used for d1 and c, and also d2 and c, produce a divide by zero error.  See the operations performed on lines 55, 58, and then 59.  

I don't know the chisquare test operation well enough to identify any errors in the code, but essectially the values of c are very small relative to the d1 and d2 values, producing zeros for the internal variables n_x and n_y. divide by (n_x+n_y) appears in the chisq calculation, so this obviously is a divide by zero error, or NaN.

I have access to a copy of matlab and it appears they do not have this function.  Can you point to some other implementation of the test that we can compare results?

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