Tom: That's a good question. AIC, as i'm sure you know, is usually calculated as 2k-2ln(L), where k is the number of free parameters in the model, and L is the log-likelihood of the model. The goal of AIC--and the reason one normally tries to select a model with minimal AIC--is to minimize what's referred to as the Kullback-Leibler distance between the distribution of your data's density from the theoretical "true" theoretical density as defined by the model. More concisely, the AIC is an index of the amount of information regarding your data that is lost when your model is used to describe it. To get back to your question, I can't say without a little more information why the AIC's your referring to are negative (but perhaps it's an issue of using the log-likelihood instead of the negative log- likelihood), but my first instinct is that it doesn't matter. I would go with the AIC that is closest to zero. I hope that helps.
Kyle H. Ambert Graduate Student, Dept. Behavioral Neuroscience Oregon Health & Science University [EMAIL PROTECTED] On Aug 3, 2007, at 8:41 AM, Tom Willems wrote: > Dear fellow R-ussers, > I have a question about the Akaike Information Criterion in the R > output. > Normally you would want it to be as small as possible, yet when i > check up > the information in my study books, the AIC is usually displayed as a > negative number. In the exercises it is given as " - AIC ". > R displays it as a positive number, does this mean that a large "AIC" > gives a small " - AIC ", so the bigger the better? > > > Kind regards, > Tom. > > > > > Tom Willems > CODA-CERVA-VAR > Department of Virology > Epizootic Diseases Section > Groeselenberg 99 > B-1180 Ukkel > > Tel.: +32 2 3790522 > Fax: +32 2 3790666 > E-mail: [EMAIL PROTECTED] > > www.var.fgov.be > > > > > Disclaimer: click here > [[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.