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From |
Partho Sarkar <partho.ss+lists@gmail.com> |

To |
statalist@hsphsun2.harvard.edu |

Subject |
Re: st: Regression Equation for Zero inflated negative binomial |

Date |
Tue, 20 Sep 2011 16:15:26 +0530 |

Rachel I notice you are not getting the points, so even though I have no special experience with the ZINB model, let me try to explain a basic point about this kind of regression. Please excuse me if this is too simplistic. Here your y- variable is the "count" or number of times something of interest happens in a unit of time. You assume that the "probability" of this (i.e., y=y0 for any y0) is given by the "negative binomial" probability distribution, which is defined by a parameter lambda, which in turn is determined by some characteristics of the observations. This is the left hand variable you estimate in your regression: lambda=a0+a1X1+etc. This is why you do not have any regression in the form y=b0+b1X1 etc, and no one would expect you to produce such a regression! For further clarification, I would suggest you look at these sources: http://www.ic.arizona.edu/~ce411/lectures/CountModels.ppt http://pages.stern.nyu.edu/~wgreene/Econometrics/PanelDataNotes-19.ppt http://www.ats.ucla.edu/stat/stata/output/Stata_zinb.htm http://www.ats.ucla.edu/stat/stata/dae/zinb.htm Hope this helps Partho 2011/9/20 rachel grant <rachelannegrant@gmail.com>: > Thanks to everyone but I am still very confused. I should explain, I > am not a mathematician, I dont understand mathmatical formulae, I am a > biologist. I am looking for a regression formula for ZINB but I cannot > find anything that resembles: ln (Y) + B0+B1X1 + B2X2. > Yes there are formulae in the resources you are all pointing me to but > none of them look like a regression equation, and they dont have X on > the right hand side. I can't buy expensive books... I have been > searching help file and internet resources for several months. > > thanks > Rachel Grant > > > 2011/9/19 rachel grant <rachelannegrant@gmail.com>: >> Thank you for your help. Maybe I need to explain the problem more clearly >> I have used Zero Inflated negative binomial regression in Stata to >> model some overdispersed, zero inflated count data. I got very nice >> results and also used the postestimation tools to predict Y values. >> This is included in my PhD thesis which I am about to submit. My PhD >> supervisor said as well as presenting the results (i.e cofficients, p >> values etc.) I also have to show "the model". I think by this he means >> the regression equation in the form: >> >> natural log (Y) = B0+B1X1 + B2X2.............. >> >> I cannot find out what the equation is for ZINB models and also I >> cannot find out how to make Stata display this model. >> I could just add in the coefficients myself BUT I am not sure of the >> exact formula of the model for ZINB (especially the ZI part) as I >> think it may be more complicated than the simple Poisson >> >> log e (Y) = β0 + β1Χ1 + β2Χ2 ... >> >> I have searched everywhere to find a general equation for ZINB with no >> luck and also read all the Stata help files. >> I am very confused about why this seemingly simple thing should prove >> so impossible! I am a beginner with stata, and previously only used >> simple linear regression so thank you for your patience. >> >> -- >> regards, Rachel Grant >> >> * >> * 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/ >> > > > > -- > regards, Rachel > > * > * 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/ > * * 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: Regression Equation for Zero inflated negative binomial***From:*rachel grant <rachelannegrant@gmail.com>

**Re: st: Regression Equation for Zero inflated negative binomial***From:*rachel grant <rachelannegrant@gmail.com>

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