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From |
"Lachenbruch, Peter" <Peter.Lachenbruch@oregonstate.edu> |

To |
"statalist@hsphsun2.harvard.edu" <statalist@hsphsun2.harvard.edu> |

Subject |
st: RE: zero-inflated analyses: when do you decide that is zero-inflated? |

Date |
Mon, 15 Jul 2013 15:17:46 +0000 |

My view has been if you can justify the zeros being identified you can use the two-part model. If you can't argue that, then zinp or zinb would be used. If the data look Poisson, then you can just use poisson. The usual test of variance*(n-1) divided by mean squared. Peter A. Lachenbruch, Professor (retired) ________________________________________ From: owner-statalist@hsphsun2.harvard.edu [owner-statalist@hsphsun2.harvard.edu] on behalf of Cris Dogaru (Oregon State University) [statamplus@gmail.com] Sent: Monday, July 15, 2013 7:49 AM To: statalist@hsphsun2.harvard.edu Subject: st: zero-inflated analyses: when do you decide that is zero-inflated? Dear Stata users, I couldn't find an answer to this apparently simple question: how does one decide that a distribution is zero-inflated, so that one can use zero-inflated Poisson regression or zero-inflated negative binomial regression? More concrete: my outcome variable is number of positive skin prick tests (done for 4 allergens, therefore the number has a range 0 to 4). Here are the summary tables; is this zero-inflated?.. spt_number -- number of positive (wheal>3mm) STP ----------------------------------------------------------- | Freq. Percent Valid Cum. --------------+-------------------------------------------- Valid 0 | 853 57.02 58.30 58.30 1 | 286 19.12 19.55 77.85 2 | 176 11.76 12.03 89.88 3 | 105 7.02 7.18 97.06 4 | 43 2.87 2.94 100.00 Total | 1463 97.79 100.00 Missing . | 33 2.21 Total | 1496 100.00 ----------------------------------------------------------- . fsum spt_number Variable | N Mean SD Min Max ------------+--------------------------------------------- spt_number | 1463 0.77 1.10 0.00 4.00 Many thanks Cristian Dogaru ISPM, University of Bern * * For searches and help try: * http://www.stata.com/help.cgi?search * http://www.stata.com/support/faqs/resources/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/faqs/resources/statalist-faq/ * http://www.ats.ucla.edu/stat/stata/

**Follow-Ups**:**Re: st: RE: zero-inflated analyses: when do you decide that is zero-inflated?***From:*"Cris Dogaru (Oregon State University)" <statamplus@gmail.com>

**References**:**st: zero-inflated analyses: when do you decide that is zero-inflated?***From:*"Cris Dogaru (Oregon State University)" <statamplus@gmail.com>

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