R: Recipes for Analysis, Visualization and Machine Learning

Understanding the Wilcoxon Rank Sum and Signed Rank test

The Wilcoxon Rank Sum and Signed Rank test (or Mann-Whitney-Wilcoxon) is a nonparametric test of the null hypothesis, which shows that the population distribution of two different groups are identical without assuming that the two groups are normally distributed. This recipe will show how to conduct the Wilcoxon Rank Sum and Signed Rank test in R.

Getting ready

Ensure that mtcars has already been loaded into a data frame within an R session. As the wilcox.test function is originated from the stats package, make sure the library, stats, is loaded.

How to do it...

Perform the following steps:

1. We first plot the data of mtcars with the boxplot function:

   > boxplot(mtcars$mpg~mtcars$am,ylab='mpg',names=c('automatic','manual')) ...