[R] Syntax of Levene's test

[John Fox]

Dear Paul,

The argument y is the response variable and group is a factor defining
groups (as ?levene.test says). If you have more than one factor, then you
can use interaction() to create from them a factor with levels given by the
product set of the levels of the individual factors. Here's an example

> library(car)
> data(Moore)
> attach(Moore)
> levene.test(conformity, interaction(fcategory, partner.status))
Levene's Test for Homogeneity of Variance
      Df F value Pr(>F)
group  5  1.4694 0.2219
      39               
> levels(interaction(fcategory, partner.status))
[1] "high.high"   "low.high"    "medium.high" "high.low"    "low.low"    
[6] "medium.low" 
> levels(fcategory)
[1] "high"   "low"    "medium"
> levels(partner.status)
[1] "high" "low" 

I'll add a couple of examples to the help page.

I hope this helps,
 John 

--------------------------------
John Fox
Department of Sociology
McMaster University
Hamilton, Ontario
Canada L8S 4M4
905-525-9140x23604
http://socserv.mcmaster.ca/jfox 
-------------------------------- 

> -----Original Message-----
> From: r-help-bounces at stat.math.ethz.ch 
> [mailto:r-help-bounces at stat.math.ethz.ch] On Behalf Of Paul Smith
> Sent: Wednesday, August 02, 2006 5:33 AM
> To: r-help at stat.math.ethz.ch
> Subject: [R] Syntax of Levene's test
> 
> Dear All
> 
> I am trying to use Levene's test (of package car), but I do 
> not understand quite well how to use it. '?levene.test' does 
> not unfortunately provide any example. My data are in a data 
> frame and correspond to 4 factors plus response. Could 
> someone please give me an example about how to use the command
> 
> levene.test(y, group)
> 
> ?
> 
> Thanks in advance,
> 
> Paul
> 
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