MannWhitneypróba

The Mann-Whitney U test, also known as the Wilcoxon rank-sum test or the Mann-Whitney-Wilcoxon test, is a non-parametric statistical test used to determine if two independent samples were selected from populations having the same distribution. It is often used as an alternative to the independent samples t-test when the assumptions of the t-test, such as normality of data, are not met.

The test works by ranking all the data points from both samples combined, from smallest to largest. Then, it sums the ranks for each sample separately. The Mann-Whitney U statistic is calculated based on these rank sums. The null hypothesis of the test states that the distributions of the two populations are identical. The alternative hypothesis can be that the distributions are different, or that one distribution is stochastically greater than the other.

The Mann-Whitney U test is particularly useful when dealing with ordinal data or when sample sizes are small. It is less powerful than the t-test when the assumptions for the t-test are met, but it is more robust to violations of these assumptions. Interpretation of the results involves comparing the calculated U statistic to critical values from a Mann-Whitney U distribution table or by using a p-value. A small p-value typically leads to the rejection of the null hypothesis, suggesting that there is a significant difference between the two samples.