[R] Looking for transformation to overcome heterogeneity of variances

[Peter Dalgaard]

"Paul Smith" <phhs80 at gmail.com> writes:

> On 03 Aug 2006 15:45:10 +0200, Peter Dalgaard <p.dalgaard at biostat.ku.dk> wrote:
> > > My data consists in 96 groups, each one with 10 observations. Levene's
> > > test suggests that the variances are not equal, and therefore I have
> > > tried to apply the classical transformations to have homocedasticity
> > > in order to be able to use ANOVA. Unfortunately, no transformation
> > > that I have used transforms my data into data with homocedasticity.
> > > The histogram of variances is at
> > >
> > > http://phhs80.googlepages.com/hist1.png
> > >
> > > Is someone able to suggest to me a transformation to overcome the
> > > problem of heterocedasticity?
> >
> > Not based on that information. Try the following instead:
> >
> > fit <- lm(y~g)
> > par(mfrow=c(2,2)); plot(fit)
> 
> Thanks, Peter. By 'g', you mean
> 
> factor1* factor2*factor3*factor4

If that defines your 96 groups, yes.

-- 
   O__  ---- Peter Dalgaard             Øster Farimagsgade 5, Entr.B
  c/ /'_ --- Dept. of Biostatistics     PO Box 2099, 1014 Cph. K
 (*) \(*) -- University of Copenhagen   Denmark          Ph:  (+45) 35327918
~~~~~~~~~~ - (p.dalgaard at biostat.ku.dk)                  FAX: (+45) 35327907