[R] poly() question

John Fox jfox at mcmaster.ca
Thu Nov 2 14:45:56 CET 2006

Dear Jonathan,

An alternative is to use the raw argument to poly(), possibly after
centering the predictor. This probably will work OK as long as the degree of
the polynomial isn't high.

I hope this helps,

John Fox
Department of Sociology
McMaster University
Hamilton, Ontario
Canada L8S 4M4

> -----Original Message-----
> From: r-help-bounces at stat.math.ethz.ch 
> [mailto:r-help-bounces at stat.math.ethz.ch] On Behalf Of 
> Jonathan Greenberg
> Sent: Wednesday, November 01, 2006 9:39 PM
> To: R-help
> Subject: [R] poly() question
> Besides the primary citation, "Kennedy, W. J. Jr and Gentle, 
> J. E. (1980) Statistical Computing Marcel Dekker." (which is 
> $300 and my library doesn't have it), is there any other 
> documentation on how to take a poly() object and predict "by 
> hand" new data?  E.g. What do those coefficients actually 
> mean ("The orthogonal polynomial is summarized by the 
> coefficients, which can be used to evaluate it via the 
> three-term recursion...")?  We created a GLM model with a 
> poly() term and I'm trying to apply this model in another 
> program (grass gis via mapcalc) without requiring the direct 
> link with R if at all possible.  We'd like to avoid making a 
> lookup table if at all possible.  Thanks!
> --j
> --
> Jonathan A. Greenberg, PhD
> NRC Research Associate
> NASA Ames Research Center
> MS 242-4
> Moffett Field, CA 94035-1000
> Office: 650-604-5896
> Cell: 415-794-5043
> AIM: jgrn307
> MSN: jgrn307 at hotmail.com
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