The Mann-Whitney U test is a nonparametric test that allows two groups or conditions or treatments to be compared without making the assumption that values are normally distributed. So, for example, one might compare the speed at which two different groups of people can run 100 metres, where one group has trained for six weeks and the other has not.

*Requirements*

- Two random, independent samples
- The data is continuous - in other words, it must, in principle, be possible to distinguish between values at the nth decimal place
- Scale of measurement should be ordinal, interval or ratio
- For maximum accuracy, there should be no ties, though this test - like others - has a way to handle ties

*Null Hypothesis*

The null hypothesis asserts that the *medians* of the two samples are identical.

*Equation*