I think we need some clarification here. extractAIC() is available on both systems, in the stats package in R and in the MASS library in S-PLUS. If you use extractAIC() on both systems, do you get the same ordering of models?
AIC() is also available on both systems, in the stats package again in R, and in the nlme3 library in S-PLUS. On R there are not too many classes where methods are available for both, but on S-PLUS there are a few. So what are you comparing with what? You need to say what classes of objects you are dealing with, that is very important, and what generic functions you are using for the comparison on each system. The capacity for confusion in this area is immense. Bill Venables CSIRO Laboratories PO Box 120, Cleveland, 4163 AUSTRALIA Office Phone (email preferred): +61 7 3826 7251 Fax (if absolutely necessary): +61 7 3826 7304 Mobile: (I don't have one!) Home Phone: +61 7 3286 7700 mailto:[EMAIL PROTECTED] http://www.cmis.csiro.au/bill.venables/ -----Original Message----- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On Behalf Of Alice Shelly Sent: Friday, 1 June 2007 10:07 AM To: r-help@stat.math.ethz.ch Subject: [R] AIC consistency with S-PLUS Hello- I understand that log-likelihoods are bound to differ by constants, but if i estimate AIC for a set of simple nested linear models using the following 4 methods, shouldn't at least two of them produce the same ordering of models? in R: extractAIC AIC in S-PLUS: AIC n*log(deviance(mymodel)/n) + 2*p I find it troubling that these methods all give me different answers as to the best model or even short set of models. Thanks for your comments. Alice Shelly [[alternative HTML version deleted]] ______________________________________________ R-help@stat.math.ethz.ch mailing list https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide http://www.R-project.org/posting-guide.html and provide commented, minimal, self-contained, reproducible code. ______________________________________________ R-help@stat.math.ethz.ch mailing list https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide http://www.R-project.org/posting-guide.html and provide commented, minimal, self-contained, reproducible code.