# [Rd] nobs.glm

Wincent ronggui.huang at gmail.com
Thu Apr 26 02:16:50 CEST 2012

```Thanks, Professor Ripley. It helps a lot. As a follow-up question, is
there any recommended references I can look into to figure out the
interpretation of "weights" for various families?

Best regards

Ronggui

On 24 April 2012 21:56, Prof Brian Ripley <ripley at stats.ox.ac.uk> wrote:
> 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

--
Wincent Ronggui HUANG
Sociology Department of Fudan University
PhD of City University of Hong Kong
http://homepage.fudan.edu.cn/rghuang/cv/

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