You can use offsets for other reasons than for rates. For instance, you can
use an offset as a constraint to perform a likelihood ratio test when
comparing the coefficient you may have for a particular model with some comparative
value. Suppose that you have a logistic regression coefficient of 0.15 on
variable x and you wish to test, using the likelihood ratio test, if it is
significantly equal to 0.20. You can set variable x as an offset with value 0.20
and use it as the comparison model for the LL ratio test.
This use of offsets, as well as others, can be found in Hardin & Hilbe,
"Generalized Linear Models and Extensions" (2001) Stata Press.
I should also mention that offsets have been used with dose reponse cloglog
models for some time.
Joe Hilbe
---------------------
Dear all,
I understand why one might wish to use an offset when
estimating a Poisson regression (i.e., to model rates
as opposed to counts). However, can anyone tell me
why one would use an offset when fitting a logistic or
complementary log-log model? Particularly in the
context of longitudinal (panel) data? I have gone
through all of the Stata reference manuals I own
(which, unfortunately, do not include the User's
manual) and have also tried to find the answer online.
Any feedback would be appreciated.
Thanks.
--
Jim
=====
James W. Shaw, Ph.D., Pharm.D., M.P.H.
Post-Doctoral Fellow
Tobacco Control Research Branch
Behavioral Research Program
Division of Cancer Control and Population Sciences
National Cancer Institute
Tel.: 215-852-3045
Fax: 215-542-7150
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