nonparam
Friedman test
Compare three or more paired or repeated measurements using ranks.
Requirements
- three or more repeated-measure columns
- complete matched blocks
Avoid when
- independent groups
- need covariate adjustment
Formula
Q = 12/[nk(k+1)] ΣRⱼ² − 3n(k+1)
Interpretation
Global rank-based repeated-measures difference summarized with Kendall's W.
Worked example
Compare repeated ordinal ratings collected at baseline, week 4, and week 8.
Open example datasets