[R] glm: offset in poisson

[Peter Dalgaard BSA]

"Juli G. Pausas" <juli at ceam.es> writes:

> R-users,
> 
> Can an offset term be included in a Poisson model? 
> I get an error message when trying that:
> 
> >r3o <- glm(tax ~ areal + offset(o), family=poisson)
> Error in (if (is.empty.model(mt)) glm.fit.null else glm.fit)(x = X, y = Y,  : 
>         inner loop 1; can't correct step size

Which version of R is that?

I have no trouble with simple things like 

> x1 <- rnorm(10)
> x2 <- rnorm(10)
> y <- rpois(10, exp(x1+x2))
> glm(y~x1+offset(x2),family=poisson)

Call:  glm(formula = y ~ x1 + offset(x2), family = poisson) 

Coefficients:
(Intercept)           x1  
     0.0548       0.6574  

Degrees of Freedom: 9 Total (i.e. Null);  8 Residual
Null Deviance:      9.823 
Residual Deviance: 4.018        AIC: 34.03 


You're aware that the offset needs to be on the link scale?

-- 
   O__  ---- Peter Dalgaard             Blegdamsvej 3  
  c/ /'_ --- Dept. of Biostatistics     2200 Cph. N   
 (*) \(*) -- University of Copenhagen   Denmark      Ph: (+45) 35327918
~~~~~~~~~~ - (p.dalgaard at biostat.ku.dk)             FAX: (+45) 35327907
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