On 22-Nov-03 Ted Harding wrote:
> [...]
> I have a quantitative variable Y and a 4-level ordered factor A
> (with very unequal numbers at the different levels, by the way).
>
> The command
>
> lm(Y ~ A)
>
> returns (amongst other stuff) an intercept, and coefficients
> A.L, A.Q and A.C for the Linear, Quadratic and Cubic effects.
>
> I'm trying to verify how R computes A.L, A.Q and A.C [...]
Thanks to Brian Ripley ('"contr.poly" and see MASS Ch 6'),
and Berwin Turlach (private response).
In particular, Berwin's revelation
fm <- lm(Y ~ A)
model.matrix(fm)
shows me exactly what is going on!
Best wishes to all,
Ted.
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Date: 22-Nov-03 Time: 10:35:23
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