R help - Feb 2012 - Wilcoxon test p value with one decimal place

Dear list,

Let's say I have data

 a=c(37.961,38.214,57.68)
 b=c(77.56,61.875,67.683)

wilcox.test(a,b)

the wilcoxon test only gives me a p value with one decimal place. Is this
normal? Thanks.

Jun

	[[alternative HTML version deleted]]

On Thu, Feb 16, 2012 at 10:15 AM, Jun Shen <jun.shen.ut at gmail.com>
wrote:
> Dear list,
>
> Let's say I have data
>
> ?a=c(37.961,38.214,57.68)
> ?b=c(77.56,61.875,67.683)
>
> wilcox.test(a,b)
>
> the wilcoxon test only gives me a p value with one decimal place. Is this
> normal?
No, it's discrete  :-)

(Actually, that's the answer. Read up on the Mann-Whitney test to see why).

-- Bert

Thanks.
>
> Jun
>
> ? ? ? ?[[alternative HTML version deleted]]
>
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-- 

Bert Gunter
Genentech Nonclinical Biostatistics

Internal Contact Info:
Phone: 467-7374
Website:
http://pharmadevelopment.roche.com/index/pdb/pdb-functional-groups/pdb-biostatistics/pdb-ncb-home.htm

> -----Original Message-----
> From: r-help-bounces at r-project.org [mailto:r-help-bounces at r-
> project.org] On Behalf Of Jun Shen
> Sent: Thursday, February 16, 2012 10:16 AM
> To: R-help
> Subject: [R] Wilcoxon test p value with one decimal place
> 
> Dear list,
> 
> Let's say I have data
> 
>  a=c(37.961,38.214,57.68)
>  b=c(77.56,61.875,67.683)
> 
> wilcox.test(a,b)
> 
> the wilcoxon test only gives me a p value with one decimal place. Is
> this
> normal? Thanks.
> 
> Jun
> 
Well, it depends on what your p-value is.  If you try

w <- wilcox.test(a,b)
print(w$p.value, digits=20)

you will see that it is a rounding / printing issue


Hope this is helpful,

Dan

Daniel J. Nordlund
Washington State Department of Social and Health Services
Planning, Performance, and Accountability
Research and Data Analysis Division
Olympia, WA 98504-5204