Levene's Test

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

Usage

leveneTest(y, ...)
# S3 method for class 'formula'
leveneTest(y, data, ...)
# S3 method for class 'lm'
leveneTest(y, ...)
# Default S3 method
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.

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. (2016) Applied Regression Analysis and Generalized Linear Models, Third Edition. Sage.

Fox, J. and Weisberg, S. (2019) An R Companion to Applied Regression, Third Edition, Sage.

Author

John Fox jfox@mcmaster.ca; original generic version contributed by Derek Ogle

Note

adapted from a response posted by Brian Ripley to the r-help email list.

Examples

with(Moore, leveneTest(conformity, fcategory))
#> Levene's Test for Homogeneity of Variance (center = median)
#>       Df F value Pr(>F)
#> group  2   0.046 0.9551
#>       42               
with(Moore, leveneTest(conformity, interaction(fcategory, partner.status)))
#> Levene's Test for Homogeneity of Variance (center = median)
#>       Df F value Pr(>F)
#> group  5  1.4694 0.2219
#>       39               
leveneTest(conformity ~ fcategory*partner.status, data=Moore)
#> Levene's Test for Homogeneity of Variance (center = median)
#>       Df F value Pr(>F)
#> group  5  1.4694 0.2219
#>       39               
leveneTest(lm(conformity ~ fcategory*partner.status, data=Moore))
#> Levene's Test for Homogeneity of Variance (center = median)
#>       Df F value Pr(>F)
#> group  5  1.4694 0.2219
#>       39               
leveneTest(conformity ~ fcategory*partner.status, data=Moore, center=mean)
#> Levene's Test for Homogeneity of Variance (center = mean)
#>       Df F value Pr(>F)
#> group  5  1.7915 0.1373
#>       39               
leveneTest(conformity ~ fcategory*partner.status, data=Moore, center=mean, trim=0.1)
#> Levene's Test for Homogeneity of Variance (center = mean: 0.1)
#>       Df F value Pr(>F)
#> group  5  1.7962 0.1363
#>       39