[SciPy-user] help with scipy.stats.mannwhitneyu

Bruce Southey bsouthey@gmail....
Thu Feb 5 10:32:51 CST 2009


Stéfan van der Walt wrote:
> 2009/2/5 Sturla Molden <sturla@molden.no>:
>   
>> On 2/5/2009 4:36 PM, josef.pktd@gmail.com wrote:
>>
>>     
>>> According to wikipedia, Mann-Whitney-U is the Wilcoxon rank-sum test
>>> for independent samples, just a different name.
>>>       
>> You should not trust Wikipedia.
>>     
>
> Or, you can fix the entry on Wikipedia...
>
> Stéfan
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>   
Or perhaps it is actually correct. My understanding (because I don't 
want to do it) is that these are equivalent and all major stats packages 
provide just one test. For example, Prof Brian Ripley's reply on the R list

https://stat.ethz.ch/pipermail/r-help/2005-May/071544.html

>/ I am hoping someone could shed some light into the Wilcoxon Rank Sum Test
/>/ for me?  In looking through Stats references, the Mann-Whitney U-test and
/>/ the Wilcoxon Rank Sum Test are statistically equivalent.
/
Yes, but not numerically: they differ by a constant (in the data, a 
function of the data size).

Bruce



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