Mann-Whitney test (independent samples)
The Mann-Whitney test is the non-parametric equivalent of the independent samples t-test. It should be used when the sample data are not Normally distributed, and they cannot be transformed to a Normal distribution by means of a logarithmic transformation.
Select the variables for sample 1 and sample 2. You can use the button to select variables and selection criteria in the variables list.
The Mann-Whitney test (independent samples) combines and ranks the data from sample 1 and sample 2 and calculates a statistic on the difference between the sum of the ranks of sample 1 and sample 2.
When either or both sample sizes are large (>20) then MedCalc uses the Normal approximation (Lentner, 1982) to calculate the P-value. For small sample sizes, in the absence of ties, MedCalc calculates the exact probability (Conover, 1999).
If the resulting P-value is small (P<0.05) then a statistically significant difference between the two samples can be accepted.