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From |
"Austin Nichols" <austinnichols@gmail.com> |

To |
statalist@hsphsun2.harvard.edu |

Subject |
Re: st: RE: xttobit initial value not feasible |

Date |
Mon, 14 Apr 2008 14:45:41 -0400 |

I doubt the large number of zeros is the ulitimate cause of your error message. There is probably something odd about your data. Can you run a pooled model with -tobit- instead of -xttobit-? You may also want to consider -poisson- and others in that family. On Mon, Apr 14, 2008 at 2:24 PM, sarah young <sarahyoungnew@googlemail.com> wrote: > Nick, > > Thanks so much for your reply again. you are right that 2/3 firms do > not export anything in my data, i.e. their export intensity is zero. > export intensity is measued as the ratio of exports and total sales. > Many existing literature on determinants of export intensity use > Tobit, I understand a reason is that they treat export intensity as a > censored variable. I read somewhere that for a variable like this, > i.e. with over half of the observation as zero, Tobit model is more > appropriate than xtreg or xtabond2. Is that right? Thanks a lot. > > Sarah > > > > On Mon, Apr 14, 2008 at 6:48 PM, Nick Cox <n.j.cox@durham.ac.uk> wrote: > > My point had I think nothing to do with censoring, but with the geometry > > of what you are > > asking Stata to do. > > > > Please appreciate that I don't know anything about your data, nor > > I am an economist. > > > > If I see that 2/3 of firms have zero "export intensity", then unless > > intensity > > has some special meaning, I infer from that that 2/3 firms do not export > > anything -- at least > > in the data period. > > > > sarah young > > > > > > Thanks for the response. I am just starting to learn econometrics. I > > thought that for a variable with over half of the observations are > > zero, like export intensity in my model, the variable could be treated > > as a censored variable. Or probably I am wrong? > > > > I have used xtreg and xtabond2 to estimate the model and they performed > > well. > > > > > > > > On Mon, Apr 14, 2008 at 5:31 PM, Nick Cox <n.j.cox@durham.ac.uk> wrote: > > > Consider a standard regression of your response (call it y) on any two > > > predictors. > > > Then a simplified analogue of your problem is that two-thirds of your > > > data lie on > > > the plane y = 0 and the other third lies on one side of that plane. > > > Geometrically that sounds > > > a pretty awkward situation to model. Having more predictors and using > > > tobit don't I think > > > make it any easier. > > > > > > There is no positive suggestion embedded here, just a thought that the > > > message doesn't sound that > > > surprising in such a light. > > > > > > Nick > > > n.j.cox@durham.ac.uk > > > > > > sarah young > > > > > > I have been trying to run xttobit without success. The problem is > > > "initial value not feasible". > > > > > > I have a panel of more than 4000 firms for 15 years, which altoghther > > > is about 62,000 firm-year observations. The dependent variable is > > > export intensity, two thirds of which are zeros. So I chose to use > > > Tobit model. The model is on the determinants of export intensity, > > > theoretically the choosing of the independent variables is fine, which > > > include TFP, age, size, R&D intensity etc, as well as year and > > > industry dummies. I have tried by using different sets of independent > > > variables, for example, including only one variable on the right side, > > > excluding year and industry dummies, all of these not working and the > > > message was the same, "initial value not feasible." > > > > > > I have searched on Statalist archive and found this thread: > > > http://www.stata.com/statalist/archive/2007-05/msg01036.html > > > > > > I tried to solve the problem according to the suggestions in the > > > thread but still it is not working. Could anyone give some advice? > > > What are the possible problems behind this? How to solve them? * * For searches and help try: * http://www.stata.com/support/faqs/res/findit.html * http://www.stata.com/support/statalist/faq * http://www.ats.ucla.edu/stat/stata/

**Follow-Ups**:**RE: st: RE: xttobit initial value not feasible***From:*"Lachenbruch, Peter" <Peter.Lachenbruch@oregonstate.edu>

**Re: st: RE: xttobit initial value not feasible***From:*David Jacobs <jacobs.184@sociology.osu.edu>

**References**:**st: xttobit initial value not feasible***From:*"sarah young" <sarahyoungnew@googlemail.com>

**st: RE: xttobit initial value not feasible***From:*"Nick Cox" <n.j.cox@durham.ac.uk>

**Re: st: RE: xttobit initial value not feasible***From:*"sarah young" <sarahyoungnew@googlemail.com>

**RE: st: RE: xttobit initial value not feasible***From:*"Nick Cox" <n.j.cox@durham.ac.uk>

**Re: st: RE: xttobit initial value not feasible***From:*"sarah young" <sarahyoungnew@googlemail.com>

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