R- Non-parametric Tests (Mann-Whitney U-test)
Get R-nonparametric (Mann-Whitney U-test) data analysis help from qualified professionals. The Mann-Whitney U-test compares the median values of two samples. It is a non-parametric test and is used when we cannot make any assumptions about the population from which the sample is drawn. For instance, we cannot assume normality of the distribution. The Mann-Whitney U-test in R is commonly associated with the Wilcoxon Rank Sum test; hence the procedure in R is wilcox.test(), given by the formula:
wilcox.test(x, y, alternative, mu, paired)
whereby; x= a numerical sample
y= a second numerical sample
alternative= the default setting for comparing means is “two.sided”. You can also enter “less” or “greater” as a value.
mu= The actual median value (or median difference). The default value is 0.
Paired= paired = FALSE, is the default value. This presupposes that the samples are independent. In matched pair test, the option paired = true, is utilized.
If there are any tied ranks, you might receive a warning concerning exact p-values. You can disregard this warning