Wilcoxon V = 0

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Wilcoxon V = 0

Naomikb
I am running a pairwise wilcoxon signed rank test, and I am not sure how to interpret the result.  I would like to see if there is a difference between the values in conditions a and b. It doesn't seem possible to have a V = 0, but a significant p value. Am I doing something wrong?

The command I used is this:
 wilcox.test(x=a$x,y=b$x,paired=TRUE)


The output looks like this:
        Wilcoxon signed rank test

data:  a$x and b$x
V = 0, p-value = 0.0009766
alternative hypothesis: true location shift is not equal to 0

The raw data is here:

a
   participant        condition            x
34           1 fused.mu.control           315.5677
35           2 fused.mu.control           516.8781
36           3 fused.mu.control           362.8108
37           4 fused.mu.control           482.6022
38           5 fused.mu.control           423.6593
39           6 fused.mu.control           404.9358
40           8 fused.mu.control           342.7314
41           9 fused.mu.control           466.7561
42          10 fused.mu.control           467.5002
43          11 fused.mu.control           434.0221
44          12 fused.mu.control           480.2990


b
   participant   condition      x
45           1 fused.multi           373.0648
46           2 fused.multi           517.5159
47           3 fused.multi           390.2658
48           4 fused.multi           497.2303
49           5 fused.multi           519.7867
50           6 fused.multi           499.7950
51           8 fused.multi           345.8077
52           9 fused.multi           479.1607
53          10 fused.multi           539.5856
54          11 fused.multi           446.9569
55          12 fused.multi           569.5171
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Re: Wilcoxon V = 0

arun kirshna
This post has NOT been accepted by the mailing list yet.
Hello,

Your question is whether it is possible to have V=0.
Check this link.  (http://www.r-bloggers.com/wilcoxon-signed-rank-test/).  If you calculate V based on the method shown in the link, you will get 0.
 diff1<-a$x-b$x
 diff1<-diff1[diff1!=0]
diff1.rank<-rank(abs(diff1))
diff1.rank.sign<-diff1.rank*sign(diff1)
ranks.pos<-sum(diff1.rank.sign[diff1.rank.sign>0])
 ranks.neg<- -sum(diff1.rank.sign[diff1.rank.sign<0])
 ranks.pos
[1] 0
> ranks.neg
[1] 66

A.K.
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Re: Wilcoxon V = 0

David Carlson
In reply to this post by Naomikb
It all depends on which order you put the values. Try this

wilcox.test(x=b$x,y=a$x,paired=TRUE)

Either one is an extreme. A non significant value would be in the middle.


----------------------------------------------
David L Carlson
Associate Professor of Anthropology
Texas A&M University
College Station, TX 77843-4352


> -----Original Message-----
> From: [hidden email] [mailto:r-help-bounces@r-
> project.org] On Behalf Of Naomikb
> Sent: Tuesday, July 24, 2012 4:36 PM
> To: [hidden email]
> Subject: [R] Wilcoxon V = 0
>
> I am running a pairwise wilcoxon signed rank test, and I am not sure
> how to
> interpret the result.  I would like to see if there is a difference
> between
> the values in conditions a and b. It doesn't seem possible to have a V
> = 0,
> but a significant p value. Am I doing something wrong?
>
> The command I used is this:
>  wilcox.test(x=a$x,y=b$x,paired=TRUE)
>
>
> The output looks like this:
> Wilcoxon signed rank test
>
> data:  a$x and b$x
> V = 0, p-value = 0.0009766
> alternative hypothesis: true location shift is not equal to 0
>
> The raw data is here:
>
> a
>    participant        condition            x
> 34           1 fused.mu.control           315.5677
> 35           2 fused.mu.control           516.8781
> 36           3 fused.mu.control           362.8108
> 37           4 fused.mu.control           482.6022
> 38           5 fused.mu.control           423.6593
> 39           6 fused.mu.control           404.9358
> 40           8 fused.mu.control           342.7314
> 41           9 fused.mu.control           466.7561
> 42          10 fused.mu.control           467.5002
> 43          11 fused.mu.control           434.0221
> 44          12 fused.mu.control           480.2990
>
>
> b
>    participant   condition      x
> 45           1 fused.multi           373.0648
> 46           2 fused.multi           517.5159
> 47           3 fused.multi           390.2658
> 48           4 fused.multi           497.2303
> 49           5 fused.multi           519.7867
> 50           6 fused.multi           499.7950
> 51           8 fused.multi           345.8077
> 52           9 fused.multi           479.1607
> 53          10 fused.multi           539.5856
> 54          11 fused.multi           446.9569
> 55          12 fused.multi           569.5171
>
>
>
>
> --
> View this message in context: http://r.789695.n4.nabble.com/Wilcoxon-V-
> 0-tp4637675.html
> Sent from the R help mailing list archive at Nabble.com.
>
> ______________________________________________
> [hidden email] mailing list
> https://stat.ethz.ch/mailman/listinfo/r-help
> PLEASE do read the posting guide http://www.R-project.org/posting-
> guide.html
> and provide commented, minimal, self-contained, reproducible code.

______________________________________________
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Re: Wilcoxon V = 0

Naomikb
This is very helpful, thank you. 

On Tue, Jul 24, 2012 at 10:54 PM, David Carlson [via R] <[hidden email]> wrote:
It all depends on which order you put the values. Try this

wilcox.test(x=b$x,y=a$x,paired=TRUE)

Either one is an extreme. A non significant value would be in the middle.


----------------------------------------------
David L Carlson
Associate Professor of Anthropology
Texas A&M University
College Station, TX 77843-4352


> -----Original Message-----
> From: [hidden email] [mailto:[hidden email]
> project.org] On Behalf Of Naomikb
> Sent: Tuesday, July 24, 2012 4:36 PM
> To: [hidden email]

> Subject: [R] Wilcoxon V = 0
>
> I am running a pairwise wilcoxon signed rank test, and I am not sure
> how to
> interpret the result.  I would like to see if there is a difference
> between
> the values in conditions a and b. It doesn't seem possible to have a V
> = 0,
> but a significant p value. Am I doing something wrong?
>
> The command I used is this:
>  wilcox.test(x=a$x,y=b$x,paired=TRUE)
>
>
> The output looks like this:
> Wilcoxon signed rank test
>
> data:  a$x and b$x
> V = 0, p-value = 0.0009766
> alternative hypothesis: true location shift is not equal to 0
>
> The raw data is here:
>
> a
>    participant        condition            x
> 34           1 fused.mu.control           315.5677
> 35           2 fused.mu.control           516.8781
> 36           3 fused.mu.control           362.8108
> 37           4 fused.mu.control           482.6022
> 38           5 fused.mu.control           423.6593
> 39           6 fused.mu.control           404.9358
> 40           8 fused.mu.control           342.7314
> 41           9 fused.mu.control           466.7561
> 42          10 fused.mu.control           467.5002
> 43          11 fused.mu.control           434.0221
> 44          12 fused.mu.control           480.2990
>
>
> b
>    participant   condition      x
> 45           1 fused.multi           373.0648
> 46           2 fused.multi           517.5159
> 47           3 fused.multi           390.2658
> 48           4 fused.multi           497.2303
> 49           5 fused.multi           519.7867
> 50           6 fused.multi           499.7950
> 51           8 fused.multi           345.8077
> 52           9 fused.multi           479.1607
> 53          10 fused.multi           539.5856
> 54          11 fused.multi           446.9569
> 55          12 fused.multi           569.5171
>
>
>
>
> --
> View this message in context: http://r.789695.n4.nabble.com/Wilcoxon-V-
> 0-tp4637675.html
> Sent from the R help mailing list archive at Nabble.com.
>
> ______________________________________________
> [hidden email] mailing list
> https://stat.ethz.ch/mailman/listinfo/r-help
> PLEASE do read the posting guide http://www.R-project.org/posting-
> guide.html
> and provide commented, minimal, self-contained, reproducible code.

______________________________________________
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and provide commented, minimal, self-contained, reproducible code.



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Re: Wilcoxon V = 0

Peter Ehlers
In reply to this post by Naomikb
On 2012-07-24 14:36, Naomikb wrote:
> I am running a pairwise wilcoxon signed rank test, and I am not sure how to
> interpret the result.  I would like to see if there is a difference between
> the values in conditions a and b. It doesn't seem possible to have a V = 0,
> but a significant p value. Am I doing something wrong?

Not understanding the test?
V is the sum of the ranks[*] of those pairs for which a$x > b$x;
there are none, so V = 0. You can check the p-value with the
[dp]signedrank() function.

[*] ranks of absolute differences.

Peter Ehlers

>
> The command I used is this:
>   wilcox.test(x=a$x,y=b$x,paired=TRUE)
>
>
> The output looks like this:
> Wilcoxon signed rank test
>
> data:  a$x and b$x
> V = 0, p-value = 0.0009766
> alternative hypothesis: true location shift is not equal to 0
>
> The raw data is here:
>
> a
>     participant        condition            x
> 34           1 fused.mu.control           315.5677
> 35           2 fused.mu.control           516.8781
> 36           3 fused.mu.control           362.8108
> 37           4 fused.mu.control           482.6022
> 38           5 fused.mu.control           423.6593
> 39           6 fused.mu.control           404.9358
> 40           8 fused.mu.control           342.7314
> 41           9 fused.mu.control           466.7561
> 42          10 fused.mu.control           467.5002
> 43          11 fused.mu.control           434.0221
> 44          12 fused.mu.control           480.2990
>
>
> b
>     participant   condition      x
> 45           1 fused.multi           373.0648
> 46           2 fused.multi           517.5159
> 47           3 fused.multi           390.2658
> 48           4 fused.multi           497.2303
> 49           5 fused.multi           519.7867
> 50           6 fused.multi           499.7950
> 51           8 fused.multi           345.8077
> 52           9 fused.multi           479.1607
> 53          10 fused.multi           539.5856
> 54          11 fused.multi           446.9569
> 55          12 fused.multi           569.5171
>
>
>
>
> --
> View this message in context: http://r.789695.n4.nabble.com/Wilcoxon-V-0-tp4637675.html
> Sent from the R help mailing list archive at Nabble.com.
>
> ______________________________________________
> [hidden email] mailing list
> https://stat.ethz.ch/mailman/listinfo/r-help
> PLEASE do read the posting guide http://www.R-project.org/posting-guide.html
> and provide commented, minimal, self-contained, reproducible code.
>

______________________________________________
[hidden email] mailing list
https://stat.ethz.ch/mailman/listinfo/r-help
PLEASE do read the posting guide http://www.R-project.org/posting-guide.html
and provide commented, minimal, self-contained, reproducible code.