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Re: st: Maximization never converges

From   Maarten buis <>
Subject   Re: st: Maximization never converges
Date   Sun, 14 Oct 2007 12:27:38 +0100 (BST)

--- "Pavlos C. Symeou" <> wrote:
> I am running a maximisation procedure based on Wang (2002, 2003) 
> programme for the estimation of stochastic frontier models. The 
> programme can estimate cross-sectional models and panel data models
> if, according to the author, one also includes firm-specific and 
> time-specific dummies. Using my dataset, consisting of 144 countries
> and 15 years, the log-likelihood after a number of iterations (say
> takes a value which does not change over subsequent iterations (after
> more than 1500 iterations with no change I had to break the
> procedure). In addition, STATA 10 SE never finds a concave estimate
> Every single iteration is not concave. Do you have a way to overcome
> this problem?

Does the model converge if you leave out the firm and time dummies?
Also have a look at a cross tabulation of firm v. time and see if there
are sparse or empty cells. Similarly have a look at a cross tabulation
or conditinal means of these dummies with the other explanatory

Hope this helps,

Maarten L. Buis
Department of Social Research Methodology
Vrije Universiteit Amsterdam
Boelelaan 1081
1081 HV Amsterdam
The Netherlands

visiting address:
Buitenveldertselaan 3 (Metropolitan), room Z434

+31 20 5986715

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