x <- rnorm(100,10,1)
sqrtx <- sqrt(x)
y <- rbinom(100,1,0.5)

lrm(y~x+sqrtx)

works. What's the problem?

But you wrote linear+ square. Don't you mean:
lrm(Y~x+x^2)

Cheers

On Thu, Jun 3, 2010 at 6:34 AM, zhu yao <mailzhuyao@gmail.com> wrote:

> Dear r users
>
> I have a question in coding continuous variables in logistic regression.
>
> When "rcs" is used in transforming variables, sometime it gives implausible
> associations with the outcome although the model x2 is high.
>
> So what's your tips and tricks in coding continuous variables.
>
> P.S. How to code variables as linear+square in the formula such as lrm.
> lrm(y~x+sqrt(x)) can't work.
>
> Many thanks.
>
> Yao Zhu.
>
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>
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>



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