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From Thomas Neidhart <thomas.neidh...@gmail.com>
Subject Re: Weird results from ChiSquareTest
Date Fri, 18 Dec 2015 10:03:11 GMT
Hi Michael,

there are basically two different ways to use the ChiSquare test:

 * compute the chi-square test of independence (use the
chiSquareTest(long[][]) method)
 * compute the chi-square goodness of fit test (use the
chiSquareTest(double[], long[]) method)

In your example, you computed the goodness of fit test, but were expecting
the result of the test of independence.

The first provided link makes the distinction as well and you can compute
both values, getting the same result as commons-math.

Thomas


On Fri, Dec 18, 2015 at 10:34 AM, Michael Menzel <
Michael.Menzel@bioinfsys.uni-giessen.de> wrote:

> -----BEGIN PGP SIGNED MESSAGE-----
> Hash: SHA256
>
> Hi,
>
> I have a problem with the ChiSquareTest Method supplied by Apache
> Commons. I already postet it on StackOverflow, so I will just copy
> everything from there
> (
> https://stackoverflow.com/questions/34333243/apachecommons-weird-results-from-chisquaretest
> )
>
> I use the method chiSquareTest(double[] expected, long[] observed);
> But the values I get back don't make sense to me. So I tried numerous
> ChiSquare Online Calculators to find out what this function calculates.
>
> An example:
>
>     Group 1: {25,25}
>     Group 2: {30,20}
>     (Taken from Wikipedia, German Chi Square Test article)
>
> P- values from: http://www.quantpsy.org/chisq/chisq.htm and
> http://vassarstats.net/newcs.html
>
> P = 0.3149 and 0.31490284
> 0.42154642 and 0.4201
> (with and without Yates Correction)
>
>
> Apache Commons: 0.1489146731787664
>
> Code:
>
> ChiSquareTest tester = new ChiSquareTest();
>
> long[] b = {25,25};
> double[] a = {30,20};
>
> tester.chiSquareTest(a,b);
>
> Another thing I do not understand is the need to have a long and a
> double array. Why not two long arrays?
>
>
>
> Maybe one of you can help me understand the result.
>
> Thanks in advance.
>
> Michael
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