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st: offset/exposure term in poisson analysis

From   "Anne Knol" <>
Subject   st: offset/exposure term in poisson analysis
Date   Mon, 24 Jun 2002 16:54:08 -1100


I'm trying to model the rate of a certain disease (amount of cases divided by population). Am I allowed to use an exposure/offset term for the population when modelling the rate?

Furthermore, when executing the poisson command I can use an exposure term but I can't use offset (while the help file claims that these options should give the same result). Stata comments: 

exposure = exp(pop) overflows;
could not estimate constant-only model
use exposure() option for exposure = pop

When I'm using the glm command (with family=poisson) in order to be able to allow for the overdispersion of my data, I'm not allowed to use an exposure term and when trying to use offset, I get the following error message: 

initial values not feasible r(1400)

Any ideas how to solve this problem so I can include include an exposure or offset term when using glm?

Thanks (and I know, I'm a stata beginner, so I'm sorry if these are stupid questions...)


Anne Knol 
Research Fellow 
Dept. Public Health 
Wellington School of Medicine, 
PO BOX 7343, Mein St 
Wellington, New Zealand 

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