4.4.4—Paired non-parametric tests

For matched observations, calculate a difference within each pair, then apply a sign or signed-rank procedure to those differences. Pairing removes between-subject variation only when the pairing is meaningful.

Keep the order of subtraction consistent, remove zero differences as required, and do not analyse the two samples as independent if the design is paired.

Before-and-after measurements on the same 10 people produce 10 differences; the test asks whether the typical change is zero, not whether the two raw columns have equal means.

Pairing is not merely putting two samples side by side; a random pairing can add noise and invalidate the intended interpretation.