[R] lm coefficients

[Thomas Lumley]

On Tue, 3 Feb 2004, Timur Elzhov wrote:

> Dear R experts,
>
> Excuse me if my question will be stupid...
> I'd like to fit data with x^2 polynomial:
>
<snip>
> out <- lm(T ~ poly(X, 4), data = d)
> out
>   Call:
>   lm(formula = T ~ poly(X, 2), data = d)
>
>   Coefficients:
>   (Intercept)  poly(X, 2)1  poly(X, 2)2
>         9.803     -108.075       51.007
>
> So, d$T best fitted with function
>   9.803 -108.075 * X + 51.007 * X^2,


No.  The predictors are not X and X^2, but two orthogonal polynomials.
Look at the help page for poly().

	-thomas