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st: How to treat variables where all outcomes happens in one interval


From   roland andersson <rolandersson@gmail.com>
To   statalist@hsphsun2.harvard.edu
Subject   st: How to treat variables where all outcomes happens in one interval
Date   Tue, 31 Mar 2009 10:56:51 +0200

I am analysing survival in two methods of syrgery for thyroid cancer.
The international classification of stage of disease includes
tumorsize (<2, 2-4, >4 cm within the thyroid and growth outside the
thyroid, presence of distant metastases, metastases to lymphglands and
age>45 years.
In my patients all deaths have occured in patients >age 45 years. When
the dichotomised agevariable is analysed in Coxregression the HR is
very large with very large SE. There is no problem with collinearity.
How should I treat this situation? One solution would be to only
analyse according to the stage classification (which includes age >45
years for stage 3 and 4), but I would like to analyse the importance
of each element of the stageclassification. I may dichotomise with
cutoff point >50 years, but that is not correct according to the
international definition of tumourstage.

Roland Andersson
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