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

To |
statalist@hsphsun2.harvard.edu |

Subject |
Re: st: goodness of fit measure fir ivtobit |

Date |
Mon, 24 Sep 2012 12:38:50 -0400 |

Anat (Manes) Tchetchik <anatmanes@gmail.com> : Indeed, no censoring in your model. You have exactly the case I referred to when I wrote "I suspect you have a lower limit at zero which is actually a very low conditional mean rounded down to zero." Unless you believe that the Tobit model somehow correctly captures bunching at zero due to utility functions which would imply a negative demand for travel abroad, if such a thing were possible, which is implausible at best, you are much better off assuming that people with zero travel abroad simply have very low demand, and a group that has a conditional mean of 1/100000 trips will indeed have a lot of zeros observed. The -ivpois- package on SSC, and the -gmm- specifications that supersede it, are designed to allow instrumental variables in a count model, or a regression with nonnegative outcomes more generally: http://www.stata.com/meeting/boston10/boston10_nichols.pdf http://fmwww.bc.edu/repec/bocode/i/ivpois.html On Mon, Sep 24, 2012 at 10:54 AM, Anat (Manes) Tchetchik <anatmanes@gmail.com> wrote: > I haven't thought about the count model, I will definitely try to run > it! thanks much! > > On Mon, Sep 24, 2012 at 5:38 PM, Maarten Buis <maartenlbuis@gmail.com> wrote: >> That does not sound like censoring at all. I would think of this as a >> regular count model. There are examples on how to deal with such an >> iv-model in -help gmm-. >> >> Hope this helps, >> Maarten >> >> On Mon, Sep 24, 2012 at 4:11 PM, Anat (Manes) Tchetchik >> <anatmanes@gmail.com> wrote: >>> Austin Hi, >>> Thank you very much for your reply! >>> What I have as a dependent var. are 500 respondents' reports of the >>> number of times they travelled abroad to visit their friends and >>> relatives over the course of their adult lives. Some respondents yet, >>> who have relatives abroad, did not travel at all. >>> So the observations are censored at zero, with mean =2.2, max =50 and >>> stdev= 3.8. >>> Do you think in that case that the general methods of moments will be better? >>> Thanks much!!! >>> Anat >>> >>> On Sun, Sep 23, 2012 at 5:49 AM, Austin Nichols <austinnichols@gmail.com> wrote: >>>> >>>> Anat (Manes) Tchetchik <anatmanes@gmail.com>: >>>> You can always -predict- and compute the squared correlation of >>>> predictions with observed values: >>>> http://www.stata.com/support/faqs/statistics/r-squared/ >>>> but are you sure your -ivtobit- model is justified? What is the >>>> process that results in observations being censored? I suspect you >>>> have a lower limit at zero which is actually a very low conditional >>>> mean rounded down to zero--am I right? You may be better off with a >>>> -gmm- model. >>>> >>>> On Sat, Sep 22, 2012 at 5:33 PM, Anat (Manes) Tchetchik >>>> <anatmanes@gmail.com> wrote: >>>> > Dear statalisters, >>>> > >>>> > I wonder if anyone knows any goodness of fit that is appropriate for >>>> > tobit with endogenous >>>> > variables (ivtobit). Not as in "regular" tobit, stata does not report any >>>> > goodness of fit measure, any idea how to estimate such a measure? >>>> > Any response will be greatly appreciated.. * * 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/

**Follow-Ups**:**Re: st: goodness of fit measure fir ivtobit***From:*"Anat (Manes) Tchetchik" <anatmanes@gmail.com>

**References**:**st: goodness of fit measure fir ivtobit***From:*"Anat (Manes) Tchetchik" <anatmanes@gmail.com>

**Re: st: goodness of fit measure fir ivtobit***From:*Austin Nichols <austinnichols@gmail.com>

**Re: st: goodness of fit measure fir ivtobit***From:*"Anat (Manes) Tchetchik" <anatmanes@gmail.com>

**Re: st: goodness of fit measure fir ivtobit***From:*Maarten Buis <maartenlbuis@gmail.com>

**Re: st: goodness of fit measure fir ivtobit***From:*"Anat (Manes) Tchetchik" <anatmanes@gmail.com>

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