[R] Orthogonal polynomial contrasts

[Peter Dalgaard]

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])

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