[R] AIC, AICc, and K

[Spencer Graves]

      I don't know the "best" way, but the following looks like it will 
work: 

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 8.001399

      The 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
>
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-- 
Spencer Graves, PhD, Senior Development Engineer
O:  (408)938-4420;  mobile:  (408)655-4567