MannWhitneyWilcoxonTest Class 
Namespace: Accord.Statistics.Testing
[SerializableAttribute] public class MannWhitneyWilcoxonTest : HypothesisTest<MannWhitneyDistribution>
The MannWhitneyWilcoxonTest type exposes the following members.
Name  Description  

MannWhitneyWilcoxonTest 
Tests whether two samples comes from the
same distribution without assuming normality.

Name  Description  

CriticalValue 
Gets the critical value for the current significance level.
(Inherited from HypothesisTestTDistribution.)  
Hypothesis 
Gets the alternative hypothesis under test. If the test is
Significant, the null hypothesis can be rejected
in favor of this alternative hypothesis.
 
NumberOfSamples1 
Gets the number of samples in the first sample.
 
NumberOfSamples2 
Gets the number of samples in the second sample.
 
PValue 
Gets the Pvalue associated with this test.
(Inherited from HypothesisTestTDistribution.)  
Rank1 
Gets the rank statistics for the first sample.
 
Rank2 
Gets the rank statistics for the second sample.
 
RankSum1 
Gets the sum of ranks for the first sample. Often known as Ta.
 
RankSum2 
Gets the sum of ranks for the second sample. Often known as Tb.
 
Significant 
Gets whether the null hypothesis should be rejected.
(Inherited from HypothesisTestTDistribution.)  
Size 
Gets the significance level for the
test. Default value is 0.05 (5%).
(Inherited from HypothesisTestTDistribution.)  
Statistic 
Gets the test statistic.
(Inherited from HypothesisTestTDistribution.)  
Statistic1 
Gets the difference between the expected value for
the observed value of RankSum1 and its
expected value under the null hypothesis. Often known as U_a.
 
Statistic2 
Gets the difference between the expected value for
the observed value of RankSum2 and its
expected value under the null hypothesis. Often known as U_b.
 
StatisticDistribution 
Gets the distribution associated
with the test statistic.
(Inherited from HypothesisTestTDistribution.)  
Tail 
Gets the test type.
(Inherited from HypothesisTestTDistribution.) 
Name  Description  

Equals  Determines whether the specified object is equal to the current object. (Inherited from Object.)  
Finalize  Allows an object to try to free resources and perform other cleanup operations before it is reclaimed by garbage collection. (Inherited from Object.)  
GetHashCode  Serves as the default hash function. (Inherited from Object.)  
GetType  Gets the Type of the current instance. (Inherited from Object.)  
MemberwiseClone  Creates a shallow copy of the current Object. (Inherited from Object.)  
OnSizeChanged 
Called whenever the test significance level changes.
(Inherited from HypothesisTestTDistribution.)  
PValueToStatistic 
Converts a given pvalue to a test statistic.
(Overrides HypothesisTestTDistributionPValueToStatistic(Double).)  
StatisticToPValue 
Converts a given test statistic to a pvalue.
(Overrides HypothesisTestTDistributionStatisticToPValue(Double).)  
ToString 
Converts the numeric PValue of this test to its equivalent string representation.
(Inherited from HypothesisTestTDistribution.)  
ToString(String, IFormatProvider) 
Converts the numeric PValue of this test to its equivalent string representation.
(Inherited from HypothesisTestTDistribution.) 
Name  Description  

HasMethod 
Checks whether an object implements a method with the given name.
(Defined by ExtensionMethods.)  
IsEqual  Compares two objects for equality, performing an elementwise comparison if the elements are vectors or matrices. (Defined by Matrix.)  
ToT  Overloaded.
Converts an object into another type, irrespective of whether
the conversion can be done at compile time or not. This can be
used to convert generic types to numeric types during runtime.
(Defined by ExtensionMethods.)  
ToT  Overloaded.
Converts an object into another type, irrespective of whether
the conversion can be done at compile time or not. This can be
used to convert generic types to numeric types during runtime.
(Defined by Matrix.) 
The Mann–Whitney U test (also called the Mann–Whitney–Wilcoxon (MWW), Wilcoxon ranksum test, or Wilcoxon–Mann–Whitney test) is a nonparametric test of the null hypothesis that two populations are the same against an alternative hypothesis, especially that a particular population tends to have larger values than the other.
It has greater efficiency than the ttest on nonnormal distributions, such as a mixture of normal distributions, and it is nearly as efficient as the ttest on normal distributions.
The following example comes from Richard Lowry's page at http://vassarstats.net/textbook/ch11a.html. As stated by Richard, this example deals with persons seeking treatment by claustrophobia. Those persons are randomly divided into two groups, and each group receive a different treatment for the disorder.
The hypothesis would be that treatment A would more effective than B. To check this hypothesis, we can use MannWhitney's Test to compare the medians of both groups.
// Claustrophobia test scores for people treated with treatment A double[] sample1 = { 4.6, 4.7, 4.9, 5.1, 5.2, 5.5, 5.8, 6.1, 6.5, 6.5, 7.2 }; // Claustrophobia test scores for people treated with treatment B double[] sample2 = { 5.2, 5.3, 5.4, 5.6, 6.2, 6.3, 6.8, 7.7, 8.0, 8.1 }; // Create a new MannWhitneyWilcoxon's test to compare the two samples MannWhitneyWilcoxonTest test = new MannWhitneyWilcoxonTest(sample1, sample2, TwoSampleHypothesis.FirstValueIsSmallerThanSecond); double sum1 = test.RankSum1; // 96.5 double sum2 = test.RankSum2; // 134.5 double statistic1 = test.Statistic1; // 79.5 double statistic2 = test.Statistic2; // 30.5 double pvalue = test.PValue; // 0.043834132843420748 // Check if the test was significant bool significant = test.Significant; // true