järjestustest

Järjestustest, often translated as ordering test or sorting test, is a statistical test used to determine if there is a significant difference between the means of two or more groups when the data is ordinal. Ordinal data is data that can be ranked or ordered, but the differences between the ranks are not necessarily equal or quantifiable. Examples include survey responses like "strongly agree," "agree," "neutral," "disagree," and "strongly disagree," or rankings of preferences.

Unlike tests that assume interval or ratio data, such as the t-test or ANOVA, järjestustest is non-parametric. This means it does not rely on assumptions about the distribution of the data, making it suitable for data that is skewed or does not follow a normal distribution. The core principle of these tests involves ranking all observations from all groups combined and then analyzing these ranks.

A common example of a järjestustest is the Kruskal-Wallis test, which is the non-parametric equivalent of a one-way ANOVA. It is used to compare three or more independent groups. For two independent groups, the Mann-Whitney U test (also known as the Wilcoxon rank-sum test) serves a similar purpose. When comparing related or paired samples, the Wilcoxon signed-rank test is employed. These tests assess whether the observed differences in ranks between groups are likely due to chance or represent a true difference in the underlying distributions.