Description	The Mann-Whitney U test is used to compare differences between the two independent groups. The test is a Non-Parametric version of the two-sample T-test.
Why to use	To determine if the population median of the two groups differs or not.
When to use	When the dependent variable is continuous but not normally distributed.	When not to use	When the distributions of the two samples are very different. When the data consists of missing values. In which case, missing value imputation needs to be performed.
Prerequisites	Both the variables must be continuous and numeric. Group 1 and group 2 must be independent of each other. Observations are not normally distributed. Number of observations in both groups must be equal.
Input	Two numeric data groups.	Output	U statistic p Value
Statistical Methods Used	U statistic Alpha (α)	Limitations	The difference in sample sizes results in reduced power of the statistical test.

Mann Whitney U Test is located under Model Studio ( ) in Statistical Analysis below Hypothesis Test, under Non-Parametric Test in the left task pane. Use the drag-and-drop method or double-click to use the algorithm in the canvas. Click the algorithm to view and select different properties for analysis.

The system calculates the p value in this test and compares it with the alpha value.

Criteria	Interpretation
When the p-value is greater than alpha an alternative hypothesis can either be "Two-sided" or "One-sided (less than)" or "One-sided (greater than)"	As the p-value is greater than alpha, the population median of the first group equals the population median of the second group. (η1=η2)
When the p-value is less than alpha and the alternative hypothesis is equal "Two-sided"	As the p-value is less than or equal to alpha, the population median of the first group is not equal to the population median of the second group. (η1≠η2)
When the p value is less than alpha and the alternative hypothesis is equal "One-sided (less than)"	As the p value is less than or equal to alpha, the population median of the first group is less than the population median of the second group. (η1<η2)
When the p value is less than alpha and the alternative hypothesis is equal to "One-sided (greater than)"	As the p value is less than or equal to alpha, the population median of the first group is greater than the population median of the second group. (η1>η2)

Properties of Mann Whitney U Test

The available properties of the Mann Whitney U Test are shown below.

The table below describes the different properties of the Mann Whitney U Test.

Field		Description	Remark
Task Name		It is the name of the task selected on the workbook canvas.	You can click the text field to edit or modify the task's name. Space between words is not allowed in the Task Name.
Group 1		It allows you to select the independent variable.	You need to select numeric data. Only numeric columns are displayed in this dropdown.
Group 2		It allows you to select the independent variable.	You need to select numeric data. Only numeric columns are displayed in this dropdown.
Advanced	Continuity	It tells if a continuity correction should be applied or not.	The default value is True. True means that the method of continuity is asymptotic. Asymptotic means that the ratio of the two distributions approaches unity as they approach the limit or infinity.
	Alpha	It allows you to enter the alpha value or a significance level	You can modify this value. Value of alpha always lies between 0 and 1. The value 0 interprets 100% confidence on the test. The value 1 interprets 0% confidence on the test. The system cannot guarantee both scenarios; hence the values cannot be 0 and 1
	Alternative	Defines the alternative hypothesis.	The default value is Two-sided. You can modify this value. You can choose from – Two-sided - the distributions are not equal. Larger - underlying x distribution is stochastically less than the underlying y distribution. Smaller - underlying x distribution is stochastically greater than the underlying y distribution.
Node Configuration		It allows you to select the instance of the AWS server to provide control over the execution of a task in a workbook or workflow.	For more details, refer to Worker Node Configuration.

Example of Mann Whitney U Test

As a medical researcher, you wish to compare two independent drugs, Drug 1 and Drug 2 on their level of effectiveness. You use the Mann Whitney U test to determine whether the two drugs differ in their effectiveness.

The data tab shows the selected input columns. These are the two numeric data groups that are used for the comparison.
Further, the Result page is as follows.

The result page consists of the following sections:

1. Hypothesis:

This section displays Null Hypothesis and Alternative Hypothesis defined by the system.

2. Mann Whitney U Test:

This section displays the Mann Whitney U Test Rank test result. It shows value of the U Statistic, p Value and Alpha (α).

3.Interpretation:

In this example, the p value (0) is less than the alpha value (0.05); hence the null hypothesis is rejected. The rejection of the null hypothesis means that the population median of the first group differs from that of the second group.

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