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From |
"Scott Merryman" <smerryman@kc.rr.com> |

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

Subject |
st: Re: Tobit coefficients |

Date |
Tue, 23 Mar 2004 21:05:12 -0600 |

Stefan, The output of -tobit- gives the estimated coefficients that are related to the latent variable y*. It shows the effect of a change in a given x variable on the expected value of the latent variable, holding all other x variables constant. In Stata Manual example, the OLS coefficients of the latent model are compared to the estimated latent effects of the tobit model E[y*|x]. But this is just for illustration (see technical note, page 253) is you had uncensored sample there would be no reason to use a tobit model. If you are comparing the OLS marginal effects estimated on the observed data, than you would want use the expected unconditional of the observed data E[y|x]. Usually, the marginal effects of the latent variable, y*, are not of interest since it is unobserved -- we only observe y* if it above a threshold. Though why would you want to compare them to OLS coefficients, since the OLS coefficients will be inconsistent? Hope this helps, Scott ----- Original Message ----- From: "LACHENMAIER" <LACHENMAIER@ifo.de> To: <statalist@hsphsun2.harvard.edu> Sent: Tuesday, March 23, 2004 8:11 AM Subject: st: Tobit coefficients > Hi all, > > I have some problems with the output of the Tobit command. I always > thought that the coefficients presented after the tobit command are the > "pure" tobit coefficients, i.e. if I want to compare them to OLS > coefficients I have to rescale them by an adjustment factor (which > depends on whether I want to get the unconditional effect E(y | y,x), or > the conditional effect E(y | y>0,x), like described e.g. in Wooldridge > (2003, ch. 17.2). > > But then I had a closer look at the Stata manual (Stata 8) because I > wanted to learn more about the possibilities with mfx compute, > predict(). But in the first tobit example in the manual (p.252) the > tobit coefficient is directly compared to the OLS coefficient. So I am a > bit confused what the output of the tobit command really is now and how > to calculate which effects.... > > Maybe someone can help me here. > Thanks in advance > > Stefan > > PS: Sorry for posting this problem again, but I have not solved the > problem yet. Thanks! > > * > * 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/ * * 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/

**References**:**st: Tobit coefficients***From:*"LACHENMAIER" <LACHENMAIER@ifo.de>

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