tstDF <- data.frame(x=1:3, y=c(1,1,2))
fit0 <- lm(y~1, tstDF)
fitDF <- lm(y~x, tstDF)
AIC(fitDF,fit0)
df AIC
fitDF 3 5.842516
fit0 2 8.001399The function AIC with only 1 argument returns only a single number. However, given nested models, it returns a data.frame with colums df and AIC. At least in this example (and I would think in all other contexts as well), "df" is the K you want. hope this helps. Spencer Graves
Benjamin M. Osborne wrote:
How can I extract K (number of parameters) from an AIC calculation, both to report K itself and to calculate AICc? I'm aware of the conversion from AIC -> AICc, where AICc = AIC + 2K(K+1)/(n-K-1), but not sure of how K is calculated or how to extract that value from either an AIC or logLik calculation.
This is probably more of a basic statistics question than an R question, but I thank you for your help.
-Ben Osborne
-- Botany Department University of Vermont 109 Carrigan Drive Burlington, VT 05405
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