Whenever you have data that are composed of definite scores, the Wilcoxon signed rank test is preferred. When the data are not a definite score, or if the data are observational, such as “more aggressive” versus “less aggressive” then the sign test is the appropriate statistic.

When Should a Wilcoxon test be performed?

It is used to compare two sets of scores that come from the same participants. This can occur when we wish to investigate any change in scores from one time point to another, or when individuals are subjected to more than one condition.

Why would you use a Wilcoxon test?

The Wilcoxon test compares two paired groups and comes in two versions, the rank sum test and the signed rank test. The goal of the test is to determine if two or more sets of pairs are different from one another in a statistically significant manner.