At the end of this section you should be able to answer the following questions:
- When examining differences between two independent groups, which nonparametric test can be used?
- When examining differences between two dependent groups, which nonparametric test can be used?
The Mann-Whitney U Test for two Independent Samples
When examining differences between two groups, Mann-Whitney U Test is best. This test examines the differences in median scores, as well as the size of the differences. Example: Is there a difference in the median number of Facebook Friends for male and female internet users? If a researcher wanted to compare Two Related Conditions, the test to use would be the Wilcoxon Signed-Rank Test.
Interpretation for the Mann-Whitney U Test
As can be seen in the blue, there is a statistically significant difference, note the p value. The chi-squared value, and degrees of freedom are also needed for reporting. The median ranks indicate that female internet users have more Facebook Friends than male users.
The results of the Mann-Whitney U Test indicate that female internet users reported having a statistically significantly higher number of Facebook Friends (Median = 191.06) than male users (Median = 159.46; U = 5.65, p = .017).
Please click on the slides below to see an example of interpretation for the Mann-Whitney U Test.