Comparing means

Comparing means

The following tables provide guidance to the selection of the proper parametric or non-parametric statistical tests for a given data set.


Is there a difference ?

Ordinal and numerical measures
1 group N ≥ 30 One-sample t-test
N < 30 Normally distributed One-sample t-test
Not normal Sign test
2 groups Independent N ≥ 30 t-test
N < 30 Normally distributed t-test
Not normal Mann–Whitney U or Wilcoxon signed-rank test
Paired N ≥ 30 paired t-test
N < 30 Normally distributed paired t-test
Not normal Wilcoxon signed-rank test
3 or more groups Independent Normally distributed 1 factor One way anova
≥ 2 factors two or other anova
Not normal Kruskal–Wallis one-way analysis of variance by ranks
Dependent Normally distributed Repeated measures anova
Not normal Friedman two-way analysis of variance by ranks
Nominal measures
1 group np and n(1-p) ≥ 5 z-approximation
np or n(1-p) < 5 binomial
2 groups Independent np < 5 fisher exact test
np ≥ 5 chi-square test
Paired McNemar or Kappa
3 or more groups Independent np < 5 collapse categories for chi-square test
np ≥ 5 chi-square test
Dependent Cochran´s Q

See also


  • Dawson-Saunders, Beth; Trapp, Robert G. (1994). Basic & Clinical Biostatistics. Lange Medical Books. ISBN 0-8385-0542-2. 

External links

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