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From |
Nick Cox <[email protected]> |

To |
[email protected] |

Subject |
Re: st: RE: Frontier code- r(1400) error |

Date |
Wed, 6 Apr 2011 09:16:20 +0100 |

I have no specialist knowledge here, and others may have much better answers. But I think your question answers itself. The evidence is that with your model and data Stata is straining very hard to use a normal, and an exponential is a much better idea. How else can anyone interpret this information? Have you tried independent diagnostics, e.g. plotting observed vs predicted or residual vs predicted, if that makes sense? 2011/4/6 <[email protected]>: > Dear Nick, > > I tried the Cobb Douglas function at first then I include the other > variables to the model one by one. The results are much more better. > Another thing I want you to ask is about the distribution assumption. When > I use the exponential distribution, the results are significant even if > the iteration number is small (for instance: 1000). However, when I use > the half normal distribution with 1000 iteration, some of the parameters > appear as dots in the results. Sometimes increasing the iteration number > works in such cases. Is it logical to increase the iteration number? Or if > the results appear as dots even with the 1000 iteration, then it is not > needed to be continued? > > Thanks > Hande > > > >> Your original posting was >> >> http://www.stata.com/statalist/archive/2011-03/msg01715.html >> >> Evidently, that guess of 29 observations was wrong. You are still left >> with the suggestion that your model appears too complicated and that >> one strategy is to simplify it radically. When you get a model that >> does not produce estimates, you can complicate it step by step to see >> where the problem lies. >> >> Nick >> >> 2011/4/2 <[email protected]>: >>> >>> Dear Nick and Gordon >>> >>> Thank you for your advices. But Gordon says that "you have only 29 >>> observations". I might have expressed myself in an incorrect way. I have >>> 4 >>> output variables, 3 input price variables for the 29 firms. Actually I >>> have 208 observations. It seems enough to estimate the frontier, isn't >>> it >>> ? >>> >>> Thank you >>> Hande >>> >>>> Nick's answer is correct. You have 27 parameters plus the additional >>>> parameters for the efficiency error distribution and only 29 >>>> observations. This will never produce a satisfactory result. >>>> >>>> Translog frontier models can be difficult to estimate under the best >>>> of circumstances without trying to over-determine the frontier. You >>>> should start by estimating the basic log-linear Cobb-Douglas form >>>> (dropping all of the interaction terms) and then introduce >>>> interactions individually and very carefully. Even then it is >>>> unlikely that you will get any convincing results with such a small >>>> sample. * * For searches and help try: * http://www.stata.com/help.cgi?search * http://www.stata.com/support/statalist/faq * http://www.ats.ucla.edu/stat/stata/

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