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From Phil Steitz <p...@steitz.com>
Subject Re: [math] Re: Question about TestUtils.chiSquare
Date Sat, 19 Jul 2008 18:26:41 GMT
Luc Maisonobe wrote:
> First of all, please prefix your message with the name of the commons
> sub-project in brackets when using this list. It is shared by many
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>
>
> Yannick a écrit :
>   
>> Hello,
>>
>> I'm wondering why the chi-square test has this API:
>>
>> chiSquareTest(double[] expected, long[] observed) 
>>     
>
> As far as I understand, what is computed here is a Chi-square
> goodness-of-fit test or Pearson's Chi-square test. The semantics of this
> arguments were originally related to a number of real observation which
> can only be integer values.
>   
Correct.  cf the reference from the javadoc:
http://www.itl.nist.gov/div898/handbook/eda/section3/eda35f.htm
> However, looking at the implementation, it appears that the long values
> are converted to double almost everywhere, so it would at least from a
> computational point of view to convert it. I am not sure about the
> "meaning" of this as I am not a statistician.
>   
Conversion is to facilitate computation of the ChiSquare statistic.   I 
am not sure either what non-integral observed count data would mean.

What is the practical application?

Phil
> If you would like to see this behaviour changed and new signatures added
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>
> Luc
>
>   
>> -
>> I would think the type of expected and observed should be the same (for
>> example, both double, like in the situation I have, where my series
>> consists of purchase amounts on a website under two different
>> conditions). 
>>
>> Am I missing something trivial? Why is there no chiSquareTest(double[] expected,
double[] observed) test?
>>
>> Thanks!
>>
>> Yannick
>>
>>
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>>     
>
>
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