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From |
Jhilbe@aol.com |

To |
statalist@hsphsun2.harvard.edu |

Subject |
Subject: st: poisson exposure problem |

Date |
Fri, 28 Mar 2008 11:43:49 EDT |

I've never seen such a data set. Strange. The exposure variable typically gives us the time frame or area/group in which counts occur; ie the model with exposure tells us, for each covariate pattern, how many counts are in a given range of time or area/group. If the time or area/group is 0 (exposure==0), then there can be no meaningful counts. I cannot see how observations associated with an exposure of 0 can be kept in the model. Try modeling a Poisson or negative binomial model with a zero exposure. I'll bet that the algorithm will not let you proceed. I suspect that the student does not know the meaning of exposure, and needs to recode the data so that it reflects a meaningful relationship. Maybe its too early in the morning, and I'm missing something. But I don't think so. Joseph Hilbe ==================== A student comes in with a poisson model. The response variable is the number of seeds of a certain species. There is an exposure variable which is the total seeds of all species. The problem is that there are six exposure values of zero. There are three other predictor variables and 72 total observations. Is there any way of dealing with this problem other than dropping those six values? Any suggestions? - -- Phil Ender Statistical Consulting Group UCLA Academic Technology Services * **************Create a Home Theater Like the Pros. Watch the video on AOL Home. (http://home.aol.com/diy/home-improvement-eric-stromer?video=15&ncid=aolhom00030000000001) * * 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: Subject: st: poisson exposure problem***From:*"Austin Nichols" <austinnichols@gmail.com>

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