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st: continuous to categorical and determination of monotonic categories


From   cthompson@dfpm.utah.edu
To   Statalist@hsphsun2.harvard.edu
Subject   st: continuous to categorical and determination of monotonic categories
Date   Tue, 09 Dec 2003 11:11:08 -0700

Hello STATAlisters - 
The question that follows is part STATA and part statistical 
technique.  Suppose I have a continuous independent variable in 
a logistic (or cox) model and I wish to reconfigure the 
variable as a categorical (read ordinal) variable so that the 
odds ratio (hazard ratio) will be more meaningful, but before I 
categorize the variable and insert it into the model I'd like 
to determine whether the categories (e.g hospital volume:  low, 
medium, high) are monotonic relative to the outcome (e.g. shunt 
survival as measured in fractions of years) so as to establish 
some justification of linearity.  If "monotonicity" cannot be 
determined, then I understand that indicator variables must be 
created and odds ratios (hazard ratios) returned are relative 
to a referent group.  My question is two-fold:  is this an 
acceptable technique and if so, is there a straightforward and 
acceptable way to proceed using STATA??  
Many thanks in advance!
Clint Thompson   
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