[R] Wilcoxon V = 0

[Peter Ehlers]

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
>
>
>
>
> --
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