Non-parametric tests
Median - The median is the middle of a distribution: half the scores are above the median and half are below the median. The median is less sensitive to extreme scores than the mean and this makes it a better measure than the mean for highly skewed distributions. The median income is usually more informative than the mean income for example.
Interquartile range - The interquartile range (IQR) is the distance between the 75th percentile and the 25th percentile. The IQR is essentially the range of the middle 50% of the data.
Because it uses the middle 50%, the IQR is not affected by outlives or extreme values.
Spearman correlation - Spearman’s Rank Correlation is a technique used to test the direction and strength of the relationship between two variables. In other words, it’s a device to show whether any one set of numbers has an effect on another set of numbers.
Wilcox on test - The Wilcox on test compares two paired groups of data. It calculates the differences between each set of pairs, and analyses the list of differences.
Mann-Whitney test - The Mann-Whitney test is a non-parametric test for assessing whether two samples of observations come from the same distribution, testing the null hypothesis that the probability of an observation from one population exceeds the probability of an observation in a second population.
Kruskal-Wallis test - A non-parametric method for testing equality of population medians among groups, using a one-way analysis of variance by ranks.
Friedman test - The Friedman test is a non-parametric test that compares three or more paired groups.