[R] Question about mixed-effects models example (Pinheiro and Bates)

[Thomas Lumley]

On Sat, 12 Jan 2002, Shravan Vasishth wrote:

> Hi all,
>
> I'm trying to figure out the example about mixed models in the Pinheiro
> and Bates book (Mixed-Effects Models in S and S-Plus, 2000, pp. 135-137).
> One thing I don't understand is:
>
> When I run the command
>
>      fm1Orth.lm <- lm( distance ~ age, Orthodont )
>
> followed by
>
>     fm2Orth.lm <- update( fm1Orth.lm, formula = distance ~ Sex*age )
>
> and then do
>
>     summary(fm2Orth.lm)
>
> in the output, there's "SexFemale" instead of "Sex" (see below). Why?

Because that's how R displays factor constrasts.

	-thomas


Thomas Lumley			Asst. Professor, Biostatistics
tlumley at u.washington.edu	University of Washington, Seattle

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