Section 9.3: Comparing Two Independent Conditions: The Mann– Whitney U Test
Learning Objectives
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.
Write-up
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).
PowerPoint: Mann-Whitney
Please click on the slides below to see an example of interpretation for the Mann-Whitney U Test.