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st: negative binomial postest Q - how to predict X's setting Y=0?


From   "Ada Ma" <heu034@googlemail.com>
To   statalist@hsphsun2.harvard.edu
Subject   st: negative binomial postest Q - how to predict X's setting Y=0?
Date   Mon, 22 Sep 2008 01:43:42 +0100

Dear Statalisters,

I have estimated a negative binomial model using STATA's nbreg (I'm
using negbin2).  The model features a dependent variable Y, and a
bunch of explanatory variables which includes a policy explanatory
variable X.

X is continuous and can be positive or negative.  I want to calculate
the values of X's where Y would equal to zero.  Are there examples out
there that I can follow?  Are there potential pitfalls I might face?

My plan - daft but I imagine it should ensure that I avoid most
pitfalls - is to keep on increasing / decreasing X's by 1 and use the
revised X's to predict Y_hat.  If I try all the possible values (min X
to max X) then I should have a large number of predict Y_hats based on
the altered X's, if the predicted Y_hat is close to zero than the
corresponding altered X's should be the ones I'm shooting for.  I'd
love to be given suggestions on what are the smarter methods.

Thank a lot in advance!!

Ada

-- 
Ada Ma
Research Fellow
Health Economics Research Unit
University of Aberdeen, UK.
http://www.abdn.ac.uk/heru/
Tel: +44 (0) 1224 553863
Fax: +44 (0) 1224 550926
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