You're right, it is the same. using I() won't work for the same reason sqrt
don't, so :

> x2 <- x^2
> lrm(y~x+x2)

Thx for the correction.
Cheers
Joris

On Thu, Jun 3, 2010 at 6:14 PM, Bert Gunter <gunter.berton@gene.com> wrote:

> Below. -- Bert
>
> Bert Gunter
> Genentech Nonclinical Biostatistics
> --------------------------------------
> But you wrote linear+ square. Don't you mean:
> lrm(Y~x+x^2)
>
> --- I believe this is the same as lrm(Y ~ x).
> You must protect the x^2 via
>
> lrm(Y ~ x + I(x^2))
>
> ------------------------------------------
>
> --
Joris Meys
Statistical Consultant

Ghent University
Faculty of Bioscience Engineering
Department of Applied mathematics, biometrics and process control

Coupure Links 653
B-9000 Gent

tel : +32 9 264 59 87
Joris.Meys@Ugent.be
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