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Re: st: offset() option in glm models


From   Richard Williams <Richard.A.Williams.5@ND.edu>
To   "statalist@hsphsun2.harvard.edu" <statalist@hsphsun2.harvard.edu>, "statalist@hsphsun2.harvard.edu" <statalist@hsphsun2.harvard.edu>
Subject   Re: st: offset() option in glm models
Date   Thu, 14 May 2009 12:01:44 -0500

At 10:28 AM 5/14/2009, Weichle, Thomas wrote:
Dear Statalisters,
Can someone please explain the use of the offset() option in glm models?
I've searched the help menu documentation and the explanation doesn't
seem clear to me.  Thanks.

It includes the specified variable in the model with coefficient constrained to 1, which, I guess, is useful if you think a coefficient should be one. For example, maybe the var is a lagged version of the dependent variable, so in effect you are running a regression on a change score. Or, the offset option can be an alternative to the exposure option, e.g. instead of exposure(timevar) you could have offset(lntimevar). I think it is mostly a convenience as there are often other ways of achieving the same goal, e.g. you can use the constraints option.


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Richard Williams, Notre Dame Dept of Sociology
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