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From |
"Anat (Manes) Tchetchik" <anatmanes@gmail.com> |

To |
statalist@hsphsun2.harvard.edu |

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

Date |
Tue, 25 Sep 2012 15:36:22 +0200 |

Great, Thanks! On Tue, Sep 25, 2012 at 3:32 PM, Austin Nichols <austinnichols@gmail.com> wrote: > Anat (Manes) Tchetchik <anatmanes@gmail.com>: > 1. You can specify that max as exposure, but it sounds a bit odd to > me--why not just include ln(number_of_years_rel_abroad) and ln(age-17) > as predictors and let the regression estimate the coefs? If one coef > turns out to be close to one, then it looks like an exposure variable: > an exposure X just means that ln(X) enters with a coef of one > (elasticity of one). An offset X just means that X enters with a coef > of one (semi-elasticity of one). > 3. Yes, predict yhat and calculate squared corr of y and yhat as a > pseudo-R-squared. > > On Tue, Sep 25, 2012 at 7:49 AM, Anat (Manes) Tchetchik > <anatmanes@gmail.com> wrote: >> Austin hi, >> I have read the material regarding the ivpois model you have referred >> me to and ran it on my data set. The results look pretty plausible . >> Just before sticking to this model I have few last questions: >> >> 1. Can I use the exposure variable (in my case the maximum of the two >> values: respondent's adulthood years and and the no. of years his/her >> relative is staying abroad) also as an independent var.? (or given >> that I do it- I should not use the exposure option) >> >> 2. I'm not sure i understand when I should use the exposure option and >> when the offset one >> >> 3. Do I calculate goodness of fit measure using the same procedure you >> recommended earlier >> (http://www.stata.com/support/faqs/statistics/r-squared/) ? >> >> Thank you very much! >> Anat >> >> On Mon, Sep 24, 2012 at 6:38 PM, Austin Nichols <austinnichols@gmail.com> wrote: >>> >>> 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/ -- Anat Tchetchik, PhD Department of Hotel and Tourism Management Guilford Glazer Faculty of Business and Management Ben-Gurion University of the Negev P.O.Box: 653 Beer-Sheva, Israel, 84105 E-mail: anat@som.bgu.ac.il Phone 972-(0)8-6479735 Fax: 972-(0)8-6472920 Web: http://cmsprod.bgu.ac.il/Eng/som/hotelmanage/Staff/Academic/ChechikA.htm * * 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/

**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>

**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:*Austin Nichols <austinnichols@gmail.com>

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