It's not a question of a normality assumption--it's a question of whether
your variable of interest relates linearly or logarithmically to survival.
Dan Waxman
-----Original Message-----
From: [email protected]
[mailto:[email protected]] On Behalf Of Ricardo Ovaldia
Sent: Friday, February 03, 2006 3:09 PM
To: [email protected]
Subject: st: Cox PH question
Dear all,
A reviewer of a manuscript that we recently submitted to a top medical
journal stated that the "independent variable, known to be positively
skewed , be log-transformed prior to inclusion in a Cox proportional hazards
model". As far as I know there is no normality assumption for the Cox model,
additionally transforming this complicates the interpretation of the
reported hazard ratios. Am I missing something or is the reviewer wrong?
Other than for interpretation, is there another reason to transform an
independent variable in the Cox PH model?
Thank you in advance,
Ricardo.
Ricardo Ovaldia, MS
Statistician
Oklahoma City, OK
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