MOEA Framework 2.1
API Specification

org.moeaframework.util.statistics
Class WilcoxonSignedRanksTest

java.lang.Object
  extended by org.moeaframework.util.statistics.OrdinalStatisticalTest
      extended by org.moeaframework.util.statistics.WilcoxonSignedRanksTest
All Implemented Interfaces:
StatisticalTest

public class WilcoxonSignedRanksTest
extends OrdinalStatisticalTest

The Wilcoxon Signed-Ranks test determines if the population median is equal to a specified value.

Assumptions:

  1. Samples are randomly selected from the population
  2. The underlying population distribution is symmetrical

References:

  1. Sheskin, D.J. "Handbook of Parametric and Nonparametric Statistical Procedures, Third Edition." Chapman & Hall/CRC. 2004.


Field Summary
 
Fields inherited from class org.moeaframework.util.statistics.OrdinalStatisticalTest
comparator, data, numberOfGroups
 
Constructor Summary
WilcoxonSignedRanksTest(double median)
          Constructs a Wilcoxon signed ranks test with the specified median.
 
Method Summary
 void add(double value)
          Adds a new observation with the specified value.
 void add(double[] values)
          Adds several new observations with the specified values.
 double getMedian()
          Returns the value being tested against the population median.
 boolean test(double alpha)
          Returns true if the null hypothesis is rejected; false otherwise.
 
Methods inherited from class org.moeaframework.util.statistics.OrdinalStatisticalTest
add, addAll, getComparator, getNumberOfGroups, size, update
 
Methods inherited from class java.lang.Object
clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait
 

Constructor Detail

WilcoxonSignedRanksTest

public WilcoxonSignedRanksTest(double median)
Constructs a Wilcoxon signed ranks test with the specified median.

Parameters:
median - the value being tested against the population median
Method Detail

getMedian

public double getMedian()
Returns the value being tested against the population median.

Returns:
the value being tested against the population median

add

public void add(double value)
Adds a new observation with the specified value.

Parameters:
value - the value of the new observation

add

public void add(double[] values)
Adds several new observations with the specified values.

Parameters:
values - the values of the new observations

test

public boolean test(double alpha)
Returns true if the null hypothesis is rejected; false otherwise. The meaning of the null hypothesis and alternative hypothesis depends on the specific test.

The prespecified level of confidence, alpha, can be used for either one-tailed or two-tailed (directional or nondirectional) distributions, depending on the specific test. Some tests may only support specific values for alpha.

When the samples from both populations are less than 20, only alpha values of 0.05 and 0.01 are valid. This is because a table is used to accurately determine the critical values. When more than 20 samples are available, the normal approximation is used allowing any value for alpha.

Parameters:
alpha - the prespecified level of confidence
Returns:
true if the null hypothesis is rejected; false otherwise
Throws:
IllegalArgumentException - if an insufficient sampling size is provided, or if an invalid alpha value is provided

MOEA Framework 2.1
API Specification

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Licensed under the GNU Lesser General Public License.
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