nobs.glm

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

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