DescTools (version 0.99.19)

LeveneTest: Levene's Test for Homogeneity of Variance

Description

Computes Levene's test for homogeneity of variance across groups.

Usage

LeveneTest(y, ...)
"LeveneTest"(y, data, ...)
"LeveneTest"(y, ...)
"LeveneTest"(y, group, center=median, ...)

Arguments

y

response variable for the default method, or a lm or formula object. If y is a linear-model object or a formula, the variables on the right-hand-side of the model must all be factors and must be completely crossed.

group

factor defining groups.

center

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

data

a data frame for evaluating the formula.

...

arguments to be passed down, 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).

Value

returns an object meant to be printed showing the results of the test.

References

Fox, J. (2008) Applied Regression Analysis and Generalized Linear Models, Second Edition. Sage. Fox, J. and Weisberg, S. (2011) An R Companion to Applied Regression, Second Edition, Sage.

See Also

fligner.test for a rank-based (nonparametric) $k$-sample test for homogeneity of variances; mood.test for another rank-based two-sample test for a difference in scale parameters; var.test and bartlett.test for parametric tests for the homogeneity in variance.

ansari_test in package coin for exact and approximate conditional p-values for the Ansari-Bradley test, as well as different methods for handling ties.

Examples

## example from ansari.test:
## Hollander & Wolfe (1973, p. 86f):
## Serum iron determination using Hyland control sera
ramsay <- c(111, 107, 100, 99, 102, 106, 109, 108, 104, 99,
            101, 96, 97, 102, 107, 113, 116, 113, 110, 98)
jung.parekh <- c(107, 108, 106, 98, 105, 103, 110, 105, 104,
            100, 96, 108, 103, 104, 114, 114, 113, 108, 106, 99)

LeveneTest( c(ramsay, jung.parekh), 
  factor(c(rep("ramsay",length(ramsay)), rep("jung.parekh",length(jung.parekh)))))

LeveneTest( c(rnorm(10), rnorm(10, 0, 2)), factor(rep(c("A","B"),each=10)) )

## Not run: 
# # original example from package car
# 
# with(Moore, LeveneTest(conformity, fcategory))
# with(Moore, LeveneTest(conformity, interaction(fcategory, partner.status)))
# 
# LeveneTest(conformity ~ fcategory * partner.status, data = Moore)
# LeveneTest(conformity ~ fcategory * partner.status, data = Moore, center = mean)
# LeveneTest(conformity ~ fcategory * partner.status, data = Moore, center = mean, trim = 0.1)
# 
# LeveneTest(lm(conformity ~ fcategory*partner.status, data = Moore))
# ## End(Not run)