Statalist The Stata Listserver


[Date Prev][Date Next][Thread Prev][Thread Next][Date index][Thread index]

Re: st: Cox PH question


From   Ron�n Conroy <[email protected]>
To   [email protected]
Subject   Re: st: Cox PH question
Date   Fri, 3 Feb 2006 20:45:45 +0000

On 3 Feabh 2006, at 20:09, Ricardo Ovaldia wrote:

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?
The distribution of the variable will affect the ease of interpretation of the hazard ratios. Given the distribution, a hazard ratio associated with an n-fold increase in the predictor variable might make more sense than a 1-unit increase.

My own hunch is that a variable with a funny distribution might better be re-expressed in, say, deciles or quintiles. This makes the hazard ratio easily explainable. You can also do this for variables on different scales, making your hazard ratios comparable across model terms. And quantiling will deal with zero values, otherwise a tough problem on a log scale.

Ron�n Conroy
[email protected]




*
* For searches and help try:
* http://www.stata.com/support/faqs/res/findit.html
* http://www.stata.com/support/statalist/faq
* http://www.ats.ucla.edu/stat/stata/




© Copyright 1996–2024 StataCorp LLC   |   Terms of use   |   Privacy   |   Contact us   |   What's new   |   Site index