parameterization of factor in R
?contr.sum And Chapter 6 of MASS would have explained all this to you, so if you have further questions please consult it.
On Tue, 27 Dec 2005, Oana Mocila wrote:
I encountered this problem with parameterization in R: I have two factors in a regression. how about if I want to set constraint so that for each factor, the sum of their coefficients equals to zero(instead of choosing a reference category)? for example, I have factor(variable) A(with three categories) and factor(variable) B(with 4 categories), and I want to parameterize so that the sum of the three coefficients of A = 0, and sum of the four coefficients of B = 0? I mean how to do it in R?
Brian D. Ripley, ripley at stats.ox.ac.uk Professor of Applied Statistics, http://www.stats.ox.ac.uk/~ripley/ University of Oxford, Tel: +44 1865 272861 (self) 1 South Parks Road, +44 1865 272866 (PA) Oxford OX1 3TG, UK Fax: +44 1865 272595