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From |
Maarten buis <maartenbuis@yahoo.co.uk> |

To |
statalist@hsphsun2.harvard.edu |

Subject |
Re: st: Zero-inflated binomial regression |

Date |
Tue, 23 Oct 2007 14:38:59 +0100 (BST) |

--- Meryle Weinstein <mgw216@nyu.edu> wrote: > I have count data and have been doing analyses using negative > binomial regression. I've been doing reading and think that the > zero-inflated binomial regression may be more appropriate given the > number of zeros in data (243 out of 626). Two comments: 1) I assume you mean zero inflated poisson (-zip- in Stata) instead of zero-inflated binomial. 2) The negative binomial is also meant to deal with excessive zeros, although it assumes these came into existence through a different process. > The data is the count of academic after-school programs in an > elementary school zone. The zones could have zero because > they don't have any after-school programs (which is the majority of > cases) or zero because there are no academic programs. What > I don't understand and haven't been able to find in the readings is > how to choose the variables for inflate. With -zip- you assume that there are two types of districts, a type of district that will always have 0 programs, and a type of district whereby the number of programs is determined through a poisson regression (which may include 0 programs). You haven't observed the type, but only the count and this is a mixture of the two processes. The -inflate(varlist)- option tells -zip- which variables predict the type of district. So you choose those variables you think will influence the probability of being an "always zero program district". For more on this I highly recomend "Regression Models for Categorical Dependent Variables Using Stata" by J. Scott Long and Jeremy Freese. http://www.stata.com/bookstore/regmodcdvs.html Hope this helps, Maarten ----------------------------------------- Maarten L. Buis Department of Social Research Methodology Vrije Universiteit Amsterdam Boelelaan 1081 1081 HV Amsterdam The Netherlands visiting address: Buitenveldertselaan 3 (Metropolitan), room Z434 +31 20 5986715 http://home.fsw.vu.nl/m.buis/ ----------------------------------------- ___________________________________________________________ Want ideas for reducing your carbon footprint? Visit Yahoo! For Good http://uk.promotions.yahoo.com/forgood/environment.html * * 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: Zero-inflated binomial regression***From:*"Steichen, Thomas J." <SteichT@rjrt.com>

**References**:**st: Zero-inflated binomial regression***From:*"Meryle Weinstein" <mgw216@nyu.edu>

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