R-beta: Polynomials in lm/glm
Matthew R. Nelson
mrn at superh.hg.med.umich.edu
Fri Aug 15 13:44:35 CEST 1997
R users,
I was a bit surprised to find that when I attempted to add a polynomial
term to a linear model using either lm or glm as could be done in S
resulted in a fit without that term included and without warning(!!), e.g.
> lm(response ~ x + x^2, data).
As far as I can gather, there is no poly() yet in R, and if lm/glm do not
allow functions of variables as their formula arguements, is our only
option to add variables to our dataframe before using lm/glm?
> data2 <- cbind(data,x2=data$x^2)
I did search the archive for a discussion of this topic, but did not come
up with any discussion on this topic. Have I missed something?
BTW: Version 0.50 Alpha-1 (July 22, 1997)
Thanks for any help,
Matt
----------------------------------------------------------------------------
Matthew R. Nelson
Dept. of Human Genetics
University of Michigan http://www-personal.umich.edu/~ticul/
4711 Medical Science II email: ticul at umich.edu
Ann Arbor, MI 48109-0618 phone: (313) 647-3151
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