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RE: st: Biomarker with lower detection limits


From   "Nick Cox" <n.j.cox@durham.ac.uk>
To   <statalist@hsphsun2.harvard.edu>
Subject   RE: st: Biomarker with lower detection limits
Date   Wed, 18 Nov 2009 23:19:43 -0000

Please type in Stata

. findit hurdle model 

Nick 
n.j.cox@durham.ac.uk 

Eduardo Nunez

Thank you so much for your help.

Even though I know the DL, no idea about the biomarker distribution.

I may try all options suggested. However, I would like to know if
Stata perform a hurdle model?

Peter A. Lachenbruch

This sounds like an application for a two-part or hurdle model:
You want to compare the frequency of below detection limit in two
populations (or to a standard) and the continuous variable above the
detection limit.
My inclination is NOT to use imputation - you already know these are
below the detection limit, so why impute something larger than that?
I've been wary of Tobit models since I read somewhere (and I don't
remember where, darn it) that they are quite sensitive to the
normality assumption.




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