[R] predict.glm and predict.gam output

[David Winsemius]

On Jun 18, 2009, at 3:23 PM, 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?

Have you actually read the help pages for predict.glm and  
mgcv::predict.gam?

-- 
David Winsemius, MD
Heritage Laboratories
West Hartford, CT