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I don't know the text in question, but it looks like a difference in parametrisation -- the R output is just the inverse of that from the book. -- Hong Ooi Senior Research Analyst, IAG Limited 388 George St, Sydney NSW 2000 (02) 9292 1566 -----Original Message----- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On Behalf Of [EMAIL PROTECTED] Sent: Wednesday, 23 November 2005 11:28 AM To: [email protected] Subject: [R] negative binomial overdispersion question Hello, I'm a grad student in the Intelligent Transportation Systems lab at Portland State Univ. in Portland, OR, USA. I'm trying to learn the basics of R to run a negative binomial in the near future, and so I ran a test regression on roadway crash data obtained from "Statistical and Econometric Methods for Transportation Data Analysis" by Washington et al (p. 250). I ran the test (glm.nb from library MASS) and got the same output as in the text for all the parameters except the overdispersion parameter; the text lists 0.516, but R gave me an overdispersion parameter output of 1.9365. (I've attached the raw dataset, in Excel .csv format, if anyone wants to try the test. If the attachment does not go through, please email me and I'll forward it on to you.) Has anyone had similar problems with the overdispersion parameter output from R? Any thoughts on this would be much appreciated. Thanks! Kartik _______________________________________________________________________________________ The information transmitted in this message and its attachme...{{dropped}} ______________________________________________ [email protected] mailing list https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide! http://www.R-project.org/posting-guide.html
