# SuanShu, a Java numerical and statistical library

## com.numericalmethod.suanshu.stats.test.variance Class Bartlett

java.lang.Object
com.numericalmethod.suanshu.stats.test.HypothesisTest
com.numericalmethod.suanshu.stats.test.variance.Bartlett


public class Bartlettextends HypothesisTest

Bartlett's test is used to test if k samples are from populations with equal variances, hence homoscedasticity. Some statistical tests, for example ANOVA, assume that variances are equal across groups or samples. A homoscedasticity test, such as the Bartlett test, can be used to verify that assumption. Bartlett's test is sensitive to departures from normality. That is, if the samples come from non-normal distributions, then Bartlett's test may simply be testing for non-normality. The Levene and BrownForsythe tests are alternatives to the Bartlett test that are less sensitive to departures from normality.

The R equivalent function is bartlett.test.

Constructor Summary
Bartlett(double[]... samples)
Perform the Bartlett test to test for equal variances across the groups.

Method Summary
 String getAlternativeHypothesis()
Get the description of the alternative hypothesis.
 String getNullHypothesis()
Get a description of the null hypothesis.
 double pValue()
Get the p-value for the test statistics.
 double statistics()
Get the test statistics.

Methods inherited from class com.numericalmethod.suanshu.stats.test.HypothesisTest
isNullRejected, nGroups, nObs, oneSidedPvalue

Methods inherited from class java.lang.Object
clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Constructor Detail

### Bartlett

public Bartlett(double[]... samples)
Perform the Bartlett test to test for equal variances across the groups.

Parameters:
samples - samples
Method Detail

### getNullHypothesis

public String getNullHypothesis()
Description copied from class: HypothesisTest
Get a description of the null hypothesis.

Specified by:
getNullHypothesis in class HypothesisTest
Returns:
the null hypothesis description
Wikipedia: Null hypothesis

### getAlternativeHypothesis

public String getAlternativeHypothesis()
Description copied from class: HypothesisTest
Get the description of the alternative hypothesis.

Specified by:
getAlternativeHypothesis in class HypothesisTest
Returns:
the alternative hypothesis description
Wikipedia: Alternative hypothesis

### statistics

public double statistics()
Description copied from class: HypothesisTest
Get the test statistics.

Specified by:
statistics in class HypothesisTest
Returns:
the test statistics
Wikipedia: Test statistic

### pValue

public double pValue()
Description copied from class: HypothesisTest
Get the p-value for the test statistics.

Specified by:
pValue in class HypothesisTest
Returns:
the p-value