It is a statistical test used to compare two related and matched samples. If a population can not be assumed to be normally distributed, then this test may be useful with the assumption that data are paired and from the same population. Each data pair is chosen randomly. It tries to compare between sample median and hypothetical median. The boxplot below in R with the “air quality” sample data demonstrates the interpretation of the analysis using this test. boxplot(Ozone ~ Month, data = airquality) wilcox.test(Ozone ~ Month, data = airquality, subset = Month %in% c(5, 8)) Wilcoxon rank sum test with continuity correction data: Ozone by Month W = 127.5, p-value = 0.0001208 alternative hypothesis: true location shift is not equal to 0 Interpretation is this: If p-Value < 0.05, reject the null hypothesis and accept the alternative mentioned in your R code’s output.