[R] AIC in glm()

[Emmanuel Paradis]

Hi all,

I am trying to understand how is calculated the AIC returned by glm(). I
have a model object m1 which fitting results are:

> summary(m1)
[...]
(Dispersion parameter for gaussian family taken to be 3.735714)

    Null deviance: 1439.8  on 15  degrees of freedom
Residual deviance:   52.3  on 14  degrees of freedom
AIC: 70.357


Since there are 2 parameters, I would naively compute: AIC = Dev + 2*2 =
56.3, or possibly scaling the deviance by the dispersion parameter: AIC =
Dev/3.735 + 2*2 = 18.00. I do not see how is computed the value 70.357. I
have read ?extractAIC and looked in the base package, but did not find a clue.

Any help appreciated.

Emmanuel Paradis


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