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From |
"Maarten Buis" <M.Buis@fsw.vu.nl> |

To |
<statalist@hsphsun2.harvard.edu> |

Subject |
st: RE: Re: use mfx to compute marginal effects in tobit |

Date |
Wed, 8 Aug 2007 12:08:25 +0200 |

--- Zou Hong wrote: > I estimate a tobit model and then use "mfx" to compute > marginal effects of variables. Strangely, the computed > marginal effects for all the variables are the same as > the estimated cofficient in the probit model. It > seems "mfx" does not function. There are a variety of marginal effects possible and of interest after -tobit-: o the effect on the expected value of the latent variable o the effect on the expected value of the dependent, variable conditional on it being larger than the lower bound, and o the effect on the probability of being larger than the lower bound. For more on this see: (Breen 1996). By default Stata chooses the effect on the latent variable, which are exactly the same as the coefficients estimated by -tobit-. You will have to specify the -predict()- option in -mfx- to get the other marginal effects. See the example below, and -help mfx- and -help tobit postestimation- *--------- begin example ---------- sysuse auto, clear tobit mpg pric wei, ll(15) mfx mfx, pred(e(15,.)) mfx, pred(pr(15,.)) *----------- end example ---------- (For more on how to use examples I sent to the Statalist, see http://home.fsw.vu.nl/m.buis/stata/exampleFAQ.html ) Hope this helps, Maarten Richard Breen (1996) "Regression Models: Censored, Sample Selected, or Truncated Data". Thousand Oaks: Sage. ----------------------------------------- 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 http://home.fsw.vu.nl/m.buis/ ----------------------------------------- * * 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**:**st: Re: RE: Re: use mfx to compute marginal effects in tobit***From:*"Zou Hong" <hzou@ln.edu.hk>

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