> Did you read the help page?

Hi  Ista Zahn and Peter, thanks to response  me.
Well, some times on my data I have two samples with exactly values.
(not small samples)

If the mann-whitney test (wilcox.test) return a p-value = NA
Can I consider that my two sample have a p-value = 1 ???

Or there's another's cases that this test will return NA and the samples are
not the same ???

BTW, on the help ?wilcox.test

    "...Otherwise, if both 'x' and 'y' are given and 'paired' is 'FALSE',
     a Wilcoxon rank sum test (equivalent to the Mann-Whitney test: see
     the Note) is carried out..."

This is why i set the parameter PAIRED=FALSE on wicox.test.











2009/11/5 Peter Ehlers <ehlers@ucalgary.ca>


> Ambar Amarelo wrote:
>
>> Hi folks, sorry for this beginner question but what means a p-value = NA
>> on
>> a menn-whitney test?
>>
>> v1 <- c(0.022, 0.022, 0.022, 0.022, 0.022, 0.022)
>> v2 <- c(0.022, 0.022, 0.022, 0.022, 0.022)
>> wilcox.test(v1, v2, PAIRED=FALSE)
>>
>> W = 15, p-value = NA
>>
>> I know that there's no statistical difference between v1 and v2, so why my
>> p-value is not ONE ??
>>
>> Can I consider p-value= NA  as ONE ??
>> what i do when get this type of value on wilcox.test ???
>>
>>
>> PS: sorry for my bad english.
>>
>>        [[alternative HTML version deleted]]
>>
>>
> Did you read the help page? If there are ties, then a
> Normal approximation is used. So how would you do a
> Normal approximation? Try it "by hand" - you have a
> small enough amount of data.
>
> Try also a t.test() and see what message it gives you.
>
> BTW, there is no PAIRED argument to wilcox.test().
>
> --
> Peter Ehlers
> University of Calgary
>



-- 
Antigos Virus do mau,
Transformem este Nick decadente, em
Le_AmBArrrrrrr, o AmBAr Amareloooooo !

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