title: [Clinical research XVI. Differences between medians with the Mann-Whitney U test].
abstract: If you want to prove that there are differences between two groups with quantitative variables with non-normal distribution, the Mann-Whitney U test is used. This test is opposite of the Student t test that uses quantitative variables with a normal distribution. If you want to compare three or more nonrelated groups, the Kruskal-Wallis test is applied. When two related samples are compared, the Wilcoxon test is the best option (a before and after maneuver comparison); when three related samples are compared, the Friedman test is used. These tests correspond to the parametric opposing paired t test and ANOVA, respectively.
authors.affiliation: Instituto Mexicano del Seguro Social, Distrito Federal, Mexico. rivasrodolfo@gmail.com
authors.forename: Rodolfo
authors.initials: R
authors.lastname: Rivas-Ruiz
authors.forename: Jorge
authors.initials: J
authors.lastname: Moreno-Palacios
authors.forename: Juan O
authors.initials: JO
authors.lastname: Talavera
mesh_terms: D035843:Biomedical Research / Q000706:statistics & numerical data*; D018709:Statistics, Nonparametric
keywords: análisis estadístico; biomedical research; investigación biomédica; reproducibilidad de resultados; reproducibility of results; statistical analysis