[R] glm: offset

[Wensui Liu]

HI, John,
my understanding is that you should use log(...) instead of its
original scale. Below is the logic in the case of poisson reg.
log(y / offset) = x'b
=> log(y) - log(offset) = x'b
=> log(y) = x'b + log(offset)


On Sun, Mar 2, 2008 at 10:01 PM, John Sorkin
<jsorkin at grecc.umaryland.edu> wrote:
> R 2.6.0
>  Windows XP
>
>  A question about running a generalized linear model.
>
>  I am running a glm with
>  (1) a poisson distribution and a log link:
>    family=poisson(link = "log")
>  and an offset.
>  I would like to know if I should express the offset as the log of the offset value, i.e.
>  offset=log(NumUniqPt)
>  or as:
>  offset=NumUniqPt
>
>  I suspect I need to use the log, bu t I can't find any discussion of this in MASS 1994 or on the man page for glm.
>  Thanks
>  John
>
>
>  John Sorkin M.D., Ph.D.
>  Chief, Biostatistics and Informatics
>  University of Maryland School of Medicine Division of Gerontology
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WenSui Liu
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