bartlettTests function

Bartlett Tests of Homogeneity of Variances

This function extends bartlett.test to a multivariate response setting. It performs the Bartlett test of homogeneity of variances for each of a set of response variables, and prints a compact summary.

Bartlett's test is the univariate version of Box's M test for equality of covariance matrices. This function provides a univariate follow-up test to Box's M test to give one simple assessment of which response variables contribute to significant differences in variances among groups.

bartlettTests(y, ...)

## Default S3 method:
bartlettTests(y, group, ...)

## S3 method for class 'formula'
bartlettTests(y, data, ...)

## S3 method for class 'lm'
bartlettTests(y, ...)

Arguments

• y: A data frame or matrix of numeric response variables for the default method, or a model formula for a multivariate linear model, or the multivariate linear model itself. In the case of a formula or model, the variables on the right-hand-side of the model must all be factors and must be completely crossed.
• ...: other arguments, passed to bartlett.test
• group: a vector or factor object giving the group for the corresponding elements of the rows of y for the default method
• data: the data set, for the formula method

Returns

An object of classes "anova" and "data.frame", with one observation for each response variable in y.

Examples

bartlettTests(iris[,1:4], iris$Species)

data(Skulls, package="heplots")
bartlettTests(Skulls[,-1], Skulls$epoch)

# formula method
bartlettTests(cbind(mb, bh, bl, nh) ~ epoch, data=Skulls)

References

Bartlett, M. S. (1937). Properties of sufficiency and statistical tests. Proceedings of the Royal Society of London Series A, 160 , 268-282.

See Also

boxM for Box's M test for all responses together.

Author(s)

Michael Friendly