Sign Test

The sign-test is the alternative test to the Wilcoxon test for dependent data. One requirement of the Wilcoxon test is that the data needs to be at least interval scaled. For the sign test the data needs to be at least ordinal scaled.

Comparison of central tendencies of two dependent samples.

Requirements:

Dependent variable must be at least ordinal scaled.

Idea:

Dependency of the two sample data is considered by taking the differences of paired values. The signs of the individual differences are taken for the test. Under H0 the number of positive differences should approximately equal the number of negative differences. Zero-Differences are not considered in the test. The test is a simple binomial test with probability p = 0.5 for a sign to be positive and probability q = 0.5 for a sign to be negative.