What Mann - whitney u test is
The Mann-Whitney U Test is a non-parametric test used to compare two independent samples from different populations. It is used to determine if there is a statistically significant difference between the two samples. It is also known as the Wilcoxon Rank Sum Test.
Steps for Mann-Whitney U Test:
- State the null and alternative hypotheses.
The null hypothesis is that there is no difference between the two samples. The alternative hypothesis is that there is a significant difference between the two samples.
- Collect the data.
Collect data from two independent samples from different populations.
- Calculate the U statistic.
Calculate the U statistic by summing the ranks of the sample with the smaller mean.
- Compute the critical value.
Compute the critical value using a table of critical values for the Mann-Whitney U Test.
- Compare the U statistic to the critical value.
If the U statistic is less than or equal to the critical value, then the null hypothesis is rejected and there is a significant difference between the two samples.
- Interpret the results.
Interpret the results by concluding if there is a significant difference between the two samples.
Examples
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Mann-Whitney U Test is used to compare the median of two independent samples when each sample is not normally distributed.
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Mann-Whitney U Test is used to compare the medians between two groups of ordinal data when the assumptions of parametric tests are not met.
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Mann-Whitney U Test is used to compare the medians of two independent samples when both samples have small sample sizes (less than 30) in each group.
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Mann-Whitney U Test is used to compare the medians of two independent samples when the distributions of the two samples are not normal.