[math] Re: Question about TestUtils.chiSquare

[Luc Maisonobe <Lu...@free.fr>]

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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.

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.

If you would like to see this behaviour changed and new signatures added
to the existing ones, please open a feature enhancement ticket in our
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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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Re: [math] Re: Question about TestUtils.chiSquare

[Phil Steitz <ph...@steitz.com>]

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
> sub-projects and it helps people setting up filters for their topics of
> interest.
>
>
> 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
> to the existing ones, please open a feature enhancement ticket in our
> JIRA issue tracking system at http://issues.apache.org/jira/browse/MATH.
> You'll have to register to the system before being allowed to open a ticket.
>
> 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
>>
>>
>>       __________________________________________________________________
>> Be smarter than spam. See how smart SpamGuard is at giving junk email the boot with the All-new Yahoo! Mail.  Click on Options in Mail and switch to New Mail today or register for free at http://mail.yahoo.ca
>>
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>> For additional commands, e-mail: user-help@commons.apache.org
>>
>>
>>     
>
>
>
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