When the direction (and not the magnitude) of the difference within each matched paired in a paired experiment is known, the sign test can be used while the Wilcoxon signed-rank test cannot be used.

Question

Quizplus · Accepted Answer

The sign test is a non-parametric test that only requires the direction of the difference (whether it is positive or negative), while the Wilcoxon signed-rank test requires both the direction and the magnitude of the difference. Therefore, when only the direction is known, the sign test can be used but the Wilcoxon signed-rank test cannot.

When the Direction (And Not the Magnitude) of the Difference