[R] Looking for transformation to overcome heterogeneity of variances

Peter Dalgaard p.dalgaard at biostat.ku.dk
Thu Aug 3 15:45:10 CEST 2006

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

> Dear All
> 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)

   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

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