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, rip...@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
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