Hello everyone, I'm having some trouble interpreting the results of a Wilcoxon (Mann-Whitney U) test. Hope you can help.
This is the R script that I am running: a <- c(1, 1, 1, 1, 1, 1, 1, 1, 3, 1, 1, 1, 2, 1, 5, 1, 1, 1, 3, 1, 1, 1, 1, 1, 1, 3, 1, 1) b <- c(1, 2, 1, 1, 2, 3, 2, 2, 1, 2, 1, 1, 1, 2) wilcox.test(a, b, alternative="t", mu=0, exact=FALSE, paired=FALSE) #1st wilcox.test(a, b, alternative="l", mu=0, exact=FALSE, paired=FALSE) #2nd wilcox.test(a, b, alternative="g", mu=0, exact=FALSE, paired=FALSE) #3rd ... and it's returning: Wilcoxon rank sum test with continuity correction data: a and b W = 145, p-value = 0.08969 alternative hypothesis: true location shift is not equal to 0 Wilcoxon rank sum test with continuity correction data: a and b W = 145, p-value = 0.04485 alternative hypothesis: true location shift is less than 0 Wilcoxon rank sum test with continuity correction data: a and b W = 145, p-value = 0.9582 alternative hypothesis: true location shift is greater than 0 The null hypothesis is that the populations are equivalent (mu=0). The alternative hypothesis are that they differ, with the 2nd and 3rd runs of the test above considering respectively that a<b and b>a. Plus, I'm considering an alfa of 0.05. My issue is that from the first run I could not conclude that there was a difference between the two populations (0.08969>0.05), but the second run leads me to think that a<b (because 0.04485<0.05). Am I misinterpreting the results? Thanks! Filipe ______________________________________________ R-help@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.
