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st: RE: Survival analysis: finding best cut-off values

From   "Nick Cox" <>
To   <>
Subject   st: RE: Survival analysis: finding best cut-off values
Date   Tue, 6 Mar 2007 21:29:04 -0000

The practice of dividing good continuous
variables into categories is retrograde. 
See Frank Harrell's book on "Regression modeling
strategies" from Springer in 2001. 


Diego Bellavia
> I am performing a survival analysis on a dataset with many 
> variables. Multivariate cox proportional-hazard models 
> defined the best predictors (around 7 out of 270 variables). 
> I would like to give the readers some cut-off values 
> they can use in the clinical practice, so I divided the most 
> significant predictors in tertiles, create the dummy variables 
> and run Cox models for each variable (groups of dummy vars). 
> Doing so, I obtain significant/unsignificant tertiles and 
> Kaplan-Meyer graphs 
> stratified by tertiles. Thsi way works pretty well. But what 
> if I would like to find only one cut-off per variable ? 
> I thought to use ROC curves to define the best diagnostic 
> cut-offs and see if they are good also for prognosis, but 
> unfortunately not all the best
> predictors are so good also to discriminate groups of patients. 
> In conclusion my question is: there is a way to obtain the 
> best prognostic cut-off value using Cox models ? 

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