In this practical we are going to investigate how to perform a Mann Whitney test using SPSS. A Mann-Whitney test is used when we have an interval or ratio level variable measured for all observations in 2 groups and we want to test if the distribution of this variable is different in the two groups but we are unable to assume normality in both groups. It can also be used to compare an ordered categorical variable measured on two groups. It is the non-parametric equivalent of the 2-sample t-test but unlike the t-test it tests differences in the median rather than the mean. The test does not assume any distribution for the variable in either groups. To run a single test in SPSS requires that your dataset has one column containing the variable to be tested and another column of the same length with the groups identified.