An offset variable is a known component of the predicted value, in
effect it's given a coefficient of 1. It's routinely used in poisson
regression.
I've used an offset variable for two other purposes. One was to
create a table with a given set of marginals and an association
pattern. If you fit a loglinear model to (artificial) data with the
marginals you want and the log pattern of association as an offset
variable, the predicted values constitute the table you're looking
for. A second use of an offset variable is to fix the effect of a
coefficient to a value other than 0.
Hope this clarifies things a bit,
John Hendrickx
--- Joseph Coveney <[email protected]> wrote:
> Is there a catalogue of the various practical uses of the
> -offset()- option
> (available in -logit-, -probit-, -ologit-, -oprobit-, . . .)? I
> couldn't
> find any general description for its intended use(s) in the Stata
> User's
> Guide, Programming manual (didn't really expect to see anything
> there on it,
> anyway) or in the Reference manuals for the commands that have it
> as an
> option. Its description under the Options sections of the various
> commands
> that offer it is pretty brief and doesn't lend any insight as to
> what it's
> for.
>
> I knew of its use in profiling the log-likelihood to obtain
> likelihood-ratio
> confidence intervals--there's one user-written command (-logprof-)
> by Mark
> Pearce that automates the process for one estimation command
> (-logit-/-logistic-), and I've used Bill Gould's -bisect- for the
> same
> purpose for -probit- and -ologit-. But I'm not aware of anything
> comprehensive written on -offset()-'s applications beyond that.
> Today I
> stumbled across another application remeniscient to likelihood
> profiling,
> except that it doesn't search for log-likelihood values and doesn't
> calculate a deviance: hypothesis testing of a regression
> coefficient at an
> alternative-hypothesis value different from its maximum likelihood
> estimate.
>
> -findit offset- doesn't turn up anything on-target. Is there a
> source for
> the beginner that I could refer to?
>
> Joseph Coveney
>
>
>
>
>
> *
> * For searches and help try:
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> * http://www.stata.com/support/statalist/faq
> * http://www.ats.ucla.edu/stat/stata/
>
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