I'm reading a matched case-control study that used conditional logistic
regression (in STATA) to explore the predictors of being injured at work
during the prior 12 months. The analysis uses number of days worked
during the period as an offset variable presumably to adjust for
differential exposure. In conditional logistic regression the coefficient
for the offset is constrained to equal 1.
I don't understand why one would make this constraint, as opposed to using
number of days worked as another predictor variable. Is there a reference
that explains the various uses for offset variables? I wasn't able to
find a useful explanation in the STATA archives or through a general
search of the net.
Thanks in advance for any help.
Mike Frone
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