Michael,
Look at the ancova function in the HH package.
## install.packages("HH") ## if not there yet.
library(HH)
library(nlme) ## for the Orthodont data
ancova(distance ~ age*Sex, data=Orthodont)
ancova(distance ~ age+Sex, data=Orthodont)
ancova(distance ~ age, groups=Sex, data=Orthodont)
ancova(distance ~ Sex, x=age, data=Orthodont)
Rich
On Tue, Jun 22, 2010 at 12:30 PM, Michael Friendly <frien...@yorku.ca>wrote:
> Consider the following plot that shows separate regression lines ~ age for
> each subject in the Pothoff-Roy Orthodont data,
> with separate panels by Sex:
>
> library(nlme)
> #plot(Orthodont)
> xyplot(distance ~ age|Sex, data=Orthodont, type='r', groups=Subject,
> col=gray(.50),
> main="Individual linear regressions ~ age")
>
> I'd like to also show in each panel the pooled OLS regression line for each
> Sex in the corresponding panel,
> generated by the following model:
>
> Ortho.OLS <- lm(distance ~ age * Sex, data=Orthodont)
>
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