Sure -2*log(x) can be negative, and it can outweigh the k*npar term. Just do:
curve(-2*log(x)+2, 0.1, 10) # for AIC with npar = 1 abline(h=0, v=exp(1), lty=3) However, that only happens for x > exp(1) or even bigger if npar > 1. I think Olivier's real question is: do we believe in likelihoods > 1 ? Cheers, Mike. Hannu Kahra wrote: > > Olivier, > > type ?AIC and have a look at the description > > Description: > > Generic function calculating the Akaike information criterion for > one or several fitted model objects for which a log-likelihood > value can be obtained, according to the formula -2*log-likelihood > + k*npar, where npar represents the number of parameters in the > fitted model, and k = 2 for the usual AIC, or k = log(n) (n the > number of observations) for the so-called BIC or SBC (Schwarz's > Bayesian criterion). > > AIC = -2*log-likelihood + k*npar can be negative as SBC, too. > > Hannu > > On 9/7/07, Olivier MARTIN <[EMAIL PROTECTED]> wrote: >> >> Hi all, >> >> >> I obtained negative values for AIC and BIC criteria for a particular >> model that I have >> developped... >> >> I don't remember to have negative values for these crietria for others >> applications, so I am a >> little suprised... Could anyone tell me if something is wrong or his >> conclusion concerning my model? >> >> Best regards, >> Olivier. >> >> ______________________________________________ >> 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. >> > > [[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. > > -- View this message in context: http://www.nabble.com/negative-value-for-AIC-and-BIC-tf4400285.html#a12565296 Sent from the R help mailing list archive at Nabble.com. ______________________________________________ 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.