Re: [R] Identity link in tweedie

From: Peter Dunn <>
Date: Tue, 18 Dec 2007 08:38:52 +1000


> I'm using the tweedie distribution package and I cant figure out
> how to run a model using an identity link. I know I can use a log
> link by having link.power=0 and I think identity would be
> link.power=1, but I'm not sure.

Yes, that is correct.

> Furthermore when I try running it
> with link.power=1 it requires starting values which I cant manage
> to give appropriately

Without any code to see, I will guess at what is happening. The trouble with using an identity link is that the predicted means, say mu, may be negative, where as the Tweedie distributions have mu greater than zero. In using the identity link, you may be asking R to fit the impossible.

Perhaps the question you need to ask is this: Why do you need an identity link?


Dr Peter Dunn  |  dunn <at>
Faculty of Sciences, USQ;
Aust. Centre for Sustainable Catchments:

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