[R] glm: offset

From: John Sorkin <jsorkin_at_grecc.umaryland.edu>
Date: Sun, 02 Mar 2008 22:01:33 -0500


R 2.6.0
Windows XP

A question about running a generalized linear model.

I am running a glm with
(1) a poisson distribution and a log link:

   family=poisson(link = "log")
and an offset.
I would like to know if I should express the offset as the log of the offset value, i.e. offset=log(NumUniqPt)
or as:
offset=NumUniqPt

I suspect I need to use the log, bu t I can't find any discussion of this in MASS 1994 or on the man page for glm. Thanks
John

John Sorkin M.D., Ph.D.
Chief, Biostatistics and Informatics
University of Maryland School of Medicine Division of Gerontology Baltimore VA Medical Center
10 North Greene Street
GRECC (BT/18/GR)

Baltimore, MD 21201-1524
(Phone) 410-605-7119
(Fax) 410-605-7913 (Please call phone number above prior to faxing)

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