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.
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: r-help-bounces at r-project.org [mailto:r-help-bounces at r- > project.org] On Behalf Of Naomikb > Sent: Tuesday, July 24, 2012 4:36 PM > To: r-help at r-project.org > 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. > > ______________________________________________ > R-help at r-project.org 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.
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. > > ______________________________________________ > R-help at r-project.org 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. >