[R] Parameterisation of interaction terms in lm

[kjetil halvorsen]

> Using contr.sum, you'll still get one fewer coefficient than level for each
> factor, but you can fill in the missing coefficients for the interactions
> by taking the negatives of the sums of the estimates in each row and column

or even simpler by dummy.coef

Kjetil Halvorsen
> (since the estimates are constrained to sum to 0 over each coordinate).
> 
> Whether this is really of more interest than simply examining the cell
> means is another question.
> 
> I hope that this helps,
>   John
> 
> -----------------------------------------------------
> John Fox
> Department of Sociology
> McMaster University
> Hamilton, Ontario, Canada L8S 4M4
> email: jfox at mcmaster.ca
> phone: 905-525-9140x23604
> web: www.socsci.mcmaster.ca/jfox
> -----------------------------------------------------
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