R-helpers,
I am hoping to find someone who uses both R and program Stata for GLMs.
I am a beginner R user, finding my own way through; learning code etc. at the
same time as learning the statistics I need to complete my project.
What I have is the code from Stata and am trying to reproduce the same
analysis in R - my program of choice.
. glm count md ms rf sg, family(poisson)
exposure(effort) eform
I am lost at the point of finding the equivalent code for 'exposure'.
Having looked at a few forums and 'googled'. I thought 'offset', used as
offset=(log(Eff)) or the equivalent +offset(log(Eff)) would produce the
desired effect.
Incidentally my code was:
glm(Count~md+ms+rf+sg+offset(Eff),family=poisson,data=DepthHabGen)
(Making use of glm{stats})
However, offset does not seem to be equivalent to 'exposure' in Stata. As
coefficients and log likelhood estimates differ.
So I asked the following questions:
1. Do both programs produce the same results without 'exposure' i.e. glm models
Yes, log likelihoods and coefficients are the same.
2. How about using the unintuitive non logged " offset=Eff" ?
Coefficients and log likelihoods still differ.
So now I defer to those with more experience, does anyone know how to produce
the equivalent of Stata's glm 'exposure' in R?
Thank you in advance,
Columbine
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