offset

I would like to do a logistic multiple regression on a binary variate,
with what Genstat calls an offset, ie a regression variable with the
coefficient constrained=1. I'm far from home and have Splus but not R
here, but any information from either source would be very welcome. I'd
hate to have to go back to using Genstat . . .

Offsets can be given in the same way in R, ie:
use glm with binomial family and logit link; do not include your
constrained variable into the formula but use it as the optional 
offset parameter. 

Alternatively (and I suppose, that is the way you have to go in Splus), 
you can use offset() in the formula for glm.

Hope that helps, Marlene
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