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st: Roctab for classvar in descending order

Subject   st: Roctab for classvar in descending order
Date   Thu, 06 Nov 2008 14:45:35 +0100

Dear all, 

I need to study specificity and sensitivity of measures of lymphocytes.
The gold standard is measures of CD4

A subject is diseased if CD4<200 and non diseased if CD4>=200
We want to study specifity and sensitivity for different threshold of
Generally, if lymphocytes is <1200, subject is diseased.

Using the command

"roctab CD4_bin lymphocytes"

With CD4_bin=1 if CD4<200  and CD4_bin=0 if CD4>=200 

I obtain graph and table for sensitivity/specificity for threshold of
lymphocytes in ascending order.
Or I'm interested in descending order: a patient is diseased if lymphocytes
is <1200, and not >=1200

If I use 

gen inv=-1*lymphocytes
roctab CD4_bin inv

It's OK, but the table is not useful because of negative values of

Thanks for help


Ingénieur statisticien 
Service de Biostatistique des Hospices Civils de Lyon 
162 Avenue Lacassagne 
69424 Lyon Cedex 03 - France 
tél: +33 4 72 11 57 55 
fax: +33 4 72 11 51 41 

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