nobs.glm
On 24/04/2012 14:36, Wincent wrote:
Hi all, The nobs method of (MASS:::polr class) takes into account of weight, but nobs method of glm does not. I wonder what is the rationale of such design behind nobs.glm. Thanks in advance. Best Regards.
library(MASS) house.plr<- polr(Sat ~ Infl + Type + Cont, weights = Freq, data = housing) house.logit<- glm(I(Sat=='High') ~ Infl + Type + Cont, binomial,weights = Freq, data = housing) nobs(house.plr)
[1] 1681
nobs(house.logit)
[1] 72
Well, the interpretation of 'weights' for a GLM depends on the family. They may be equivalent to duplicated observations for a binomial GLM, but they are not for a Gaussian one. The nobs method for class "glm" (there is no visible nobs.glm) follows the "lm" method.
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