Hi. I'm fairly new to R and have a quick question regarding AIC, logLik and numbers of parameters. I see that there has been some correspondence on this in the past but none of the threads seem to have been satisfactorily resolved.
I have been trying to use R to obtain AIC for fitted models and then to extrapolate to AICc. For example, using simple x-y regression data, I fitted a linear regression [lm(y~x)] and an exponential curve [nls(y~A*exp(B*x))]. AICs reported for these models are based on degrees of freedom of 3 and 2, respectively. It seems clear to me that the number of parameters in both cases is 3 (two coefficients plus the error term). Consequently, I'm dubious about the values of AIC provided by R. Equally, however, I'm reluctant to base my own calculations on logLik and my own estimates of K, without first determining why R uses the degrees of freedom it does. If anyone can explain why R gives different dfs for two models each with two parameters, I should be very grateful. Thanks, Phil ______________________________________________ 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
