[R] Qualitative factors

ZABALZA-MEZGHANI Isabelle Isabelle.zabalza-mezghani at ifp.fr
Thu Nov 7 09:55:38 CET 2002

I have some doubt about how qualitative factors are coded in R. For
instance, I consider a response y, a quantitative factor x and a qualitative
factor m at 3 levels, generated as follow :



(Intercept)            x           m2           m3  
    3.96364      0.09818      0.44145      0.62291  

In literature, 2 usual implicit coding process are suggested : m1=0 or
m1=-m2-m3. Does R use one of these process ? (I've already read the R
documentation on this topic, and it is still not clear in my mind).
Furthermore, how can I make prediction using this model, I mean how should I
specify the new data (especially for m).

Thanks in advance for your help


Isabelle Zabalza-Mezghani
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