[R] wilcox.test returning 'NA' p-value

[Peter Ehlers]

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