
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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