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RE: st: Warning convergence not achieved


From   "Santos Silva, J.M.C." <jmcss@essex.ac.uk>
To   <statalist@hsphsun2.harvard.edu>
Subject   RE: st: Warning convergence not achieved
Date   Sun, 5 Aug 2012 15:42:50 +0100

Dear Ebru,

The reason may simply be that the Tobit ML estimates do not exist for your
data set. This will happen, for example, if one of your regressors is a dummy
that is equal to one only when y is equal to zero. The problem, in a different but 
related context is discussed here:
http://www.sciencedirect.com/science/article/pii/S0165176510000832
http://www.stata-journal.com/article.html?article=st0225

A simple way to check for this is to run a probit instead of a Tobit, with the same
y and the same regressors, and see if you have a "perfect predictor".

Hope this helps,

Joao


> Dear All,
> 
> When I run the tobit estimation, sometimes it gives this warning "convergence 
> not achieved". What could be the reasons? and how can I deal with that?
> 
> Best wishes
> Ebru
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