<P> The Wilcoxon signed - rank test is a non-parametric statistical hypothesis test used to compare two related samples, matched samples, or repeated measurements on a single sample to assess whether their population mean ranks differ (i.e. it is a paired difference test). It can be used as an alternative to the paired Student's t - test, t - test for matched pairs, or the t - test for dependent samples when the population cannot be assumed to be normally distributed . A Wilcoxon signed - rank test is a nonparametric test that can be used to determine whether two dependent samples were selected from populations having the same distribution . </P> <P> The test is named for Frank Wilcoxon (1892--1965) who, in a single paper, proposed both it and the rank - sum test for two independent samples (Wilcoxon, 1945). The test was popularized by Sidney Siegel (1956) in his influential textbook on non-parametric statistics . Siegel used the symbol T for a value related to, but not the same as, W (\ displaystyle W). In consequence, the test is sometimes referred to as the Wilcoxon T test, and the test statistic is reported as a value of T . </P>

What does the wilcoxon signed rank test measure