heplots (version 1.7.3)

leveneTests: Levene Tests of Homogeneity of Variances

Description

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

Usage

leveneTests(y, ...)
# S3 method for default
leveneTests(y, group, center = median, ...)
# S3 method for formula
leveneTests(y, data, ...)
# S3 method for lm
leveneTests(y, ...)

Value

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

...

arguments to be passed down to leveneTest, e.g., data for the formula and lm methods; can also be used to pass arguments to the function given by center (e.g., center=mean and trim=0.1 specify the 10% trimmed mean) other arguments.

group

a vector or factor object giving the group for the corresponding elements of the rows of y for the default method

center

The name of a function to compute the center of each group; mean gives the original Levene's (1960) test; the default, median, provides a more robust test suggested by Brown and Forsythe (1974).

data

the data set, for the formula method

Author

Michael Friendly

References

Levene, H. (1960). Robust Tests for Equality of Variances. In Olkin, I. et al. (Eds.), Contributions to Probability and Statistics: Essays in Honor of Harold Hotelling, Stanford University Press, 278-292.

Brown, M. B. & Forsythe, A. B. (1974). Robust Tests For Equality Of Variances Journal of the American Statistical Association, 69, 364-367.

See Also

leveneTest, bartlettTests

Examples

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

# handle a 1-column response?
leveneTests(iris[,1, drop=FALSE], iris$Species)

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

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

# use 10% trimmed means
leveneTests(cbind(mb, bh, bl, nh) ~ epoch, data=Skulls, trim = 0.1)


# mlm method
skulls.mod <- lm(cbind(mb, bh, bl, nh) ~ epoch, data=Skulls)
leveneTests(skulls.mod)