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From |
Christer.Thrane@hil.no |

To |
statalist@hsphsun2.harvard.edu |

Subject |
Re: st: logY, Tobit and the prediction of Y |

Date |
Wed, 23 Apr 2003 15:16:43 +0200 |

To my question below, Mathew Stalker replied: The prediction of Y from your model would simply be the exponential of the predicted logY. --- My reply: Well, according to Wooldridge, in his book Basic Econometrics (2000:202), this does not work, since the value of Y will be systematically underestimated by simply taking the exponential of logY. --- However, you should note that the log of zero is minus infinity, so in your log model no observations where Y is zero will be included. Is this really what you want? --- My reply: I solved this by setting 0 expenditures to 1 befor the log transformatiom (as I wrote in the mail). --- Christer mathew.stalker@dotecon.co m To: statalist@hsphsun2.harvard.edu Sent by: cc: owner-statalist@hsphsun2. Subject: Re: st: logY, Tobit and the prediction of Y harvard.edu 23.04.03 15:02 Please respond to statalist owner-statalist@hsphsun2.harvard.edu wrote on 23/04/2003 13:18:03: > Hi, > > My initial model is: > > Y = a + b1x1 + controls + e > > where Y is expenditures on a commodity and x1 is income. > > Since there are a lot of zeroes, I use the Tobit apporach. However, since > the log-linear model performed better than the linear, I use the former > (Before the log transformation of Y, I follow convention and set zeroes to > 1.) > > Accordingly, the estimated Tobit model is: > > logY = a + b1x1 + controls + e > > The problem: > > I want to predict the value of Y (not logY) for certain values of income > (and put it in a graph); that is, both the conditional Y (i.e. the Y given > that the threshold value of 0 was passed) and the unconditional (latent) > value of Y. > > Does anyone know how to do this? > > Best regards, > > Christer Thrane > Lillehammer University College > Norway > > > > > > * > * 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/ * * 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: logY, Tobit and the prediction of Y***From:*n j cox <n.j.cox@durham.ac.uk>

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