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.
Note
adapted from a response posted by Brian Ripley to the r-help email list.
Author(s)
John Fox jfox@mcmaster.ca; original generic version
contributed by Derek Ogle
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.