[R] predict.glm and predict.gam output

[Gavin Simpson]

On Thu, 2009-06-18 at 13:23 -0600, Anke Konrad wrote:
> Hi all,
> 
> I am currently trying to compare different plant occurrence prediction 
> maps generated in R and exported into GRASS. One of these maps was 
> generated from a glm fitted to some data, and subsequently applying this 
> glm model to a wider region using predict.glm. The outcome here was a 
> probability of occurrence. The second map I generated using a gam 
> (mgcv), however, this map seems to have assigned something like a 
> negative log-likelihood of occurrence to each raster cell in the region. 
> Since I would like to compare the two, I would like to figure out a way 
> of having the same kind of output from the "predict" functions (either 
> probability OR negative log-likelihood). Does anyone know of a way of 
> changing the output options? And if not, does anyone have any 
> suggestions of how I could deal with this issue?

Did you set type = "response" in both predict.glm and predict.gam?

It sounds like the gam predictions are still on the scale of the link
function...

G

> 
> Thank you!
> 
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