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From: Michael Menzel <Michael.Menzel@bioinfsys.uni-giessen.de>
Subject: Weird results from ChiSquareTest
Message-Id: <5673D30B.2000705@bioinfsys.uni-giessen.de>
Date: Fri, 18 Dec 2015 10:34:03 +0100
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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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