Re: [R] Orthogonal polynomial contrasts

From: Peter Dalgaard <p.dalgaard_at_biostat.ku.dk>
Date: Thu, 10 Apr 2008 14:22:55 +0200

Chris Bennett wrote:
> How do you remove one of the terms from an ordered polynomial contrast in
> your linear model. For example, I have significant terms for linear and
> cubic but not quadratic, how would i remove the quadratic term from
> lm(response~treatment)
>
> Cheers,
> Chris
>
Are you _sure_ you want to do that? The interpretation can get tricky, but if you insist, just set the contrast matrix for the term accordingly, e.g.,

C(myterm, contr.poly(4)[,-2])

-- 
   O__  ---- Peter Dalgaard             ุster Farimagsgade 5, Entr.B
  c/ /'_ --- Dept. of Biostatistics     PO Box 2099, 1014 Cph. K
 (*) \(*) -- University of Copenhagen   Denmark      Ph:  (+45) 35327918
~~~~~~~~~~ - (p.dalgaard_at_biostat.ku.dk)              FAX: (+45) 35327907

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Received on Thu 10 Apr 2008 - 12:37:12 GMT

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