Linear model - coefficients
?dummy.coef (NB: 'R' does as you tell it, and if you ask for the default contrasts you get coefficients a2 and a3, not a1 and a2. So perhaps you did something else and failed to tell us? And see the comment in ?dummy.coef about treatment contrasts.)
On Sun, 12 Jun 2011, Robert Ruser wrote:
Dear R Users, Using lm() function with categorical variable R use contrasts. Let assume that I have one X independent variable with 3-levels. Because R estimate only 2 parameters ( e.g. a1, a2) the coef function returns only 2 estimators. Is there any function or trick to get another a3 values. I know that using contrast sum (?contr.sum) I could compute a3 = -(a1+a2). But I have many independent categorical variables and I'm looking for a fast solution. Robert
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