CEVAP:

When we consider that the population of differences are symmetrical, a non-parametric test, which is called Wilcoxon signed rank, test is often more powerful than the sign test for making inferences about the population median differences MD. Hence, the main assumption of the test is that the population of differences are continuous and symmetrical. The Wilcoxon signed rank test, involves the usage of the sign and the magnitude of the rank of the differences between pairs of measurements, and it is a non-parametric alternative to the paired t test when the population distribution of the differences is not normally distributed. In this problem, the results are tied to each other, for example there is an effect, and outcomes of a variable are collected before the effect and after the effect on some observations. For example, a group of patients’ blood pressure can be measured before and after a medicine is taken. Wilcoxon Signed Rank Test does not require the normality assumption that we usually see on a parametric test.