[Biomod-commits] reporting VarImportance

Wilfried Thuiller wilfried.thuiller at ujf-grenoble.fr
Fri Mar 29 07:04:19 CET 2013

Dear Viorel,

This is a very good point. I also agree with you there are not enough papers reporting the importance of the variables. 
Make sure you do not use variables that are highly correlated BTW, else, it will not mean too much for those variables. This is important. 

> I was thinking about averaging the VarImportance scores across all my
> species and models, and present them using a bar graph with SE bars. Is it
> OK to do this across models, or does it need to be done for each model
> separately?

Barplot should indeed work perfectly fine. You may, at the same time, look at whether some groups of species have similar variable importance. 
If you have run many repetitions and PA selections (if any), you may also consider reporting (in Supp Mat) the bar plots for each models to depict whether some models are highly unstable on those aspects and some are not. 

> Also, how do I deal with the values >1, which denote negative
> correlations between the original predictions and the ones with the
> permuted variable?

I guess it depends on the questions. I am afraid I am quite uncomfortable about negative correlations in this aspect. What does it really mean? note that we do not return any statistical test. Maybe, in those cases, a statistical test will show they are not different than 1. My take on that is that either you let the 'true' value (usually, negative values are anyway close to 0) or you bound the correlations between 0 and 1 under the hypothesis that you are only interested into positive correlation, and than negative, for you, means no correlation. 
You may also consider than the ranking is importance more than the "true" value of the estimate. 

Hope it helps,


> Thank you in advance for any advice...
> Ceers,
> Viorel
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Dr. Wilfried Thuiller
Laboratoire d'Ecologie Alpine, UMR CNRS 5553
Université Joseph Fourier
BP53, 38041 Grenoble cedex 9, France
tel: +33 (0)4 76 51 44 97
fax: +33 (0)4 76 51 42 79

Email: wilfried.thuiller at ujf-grenoble.fr
Personal website: http://www.will.chez-alice.fr
Team website: http://www-leca.ujf-grenoble.fr/equipes/emabio.htm

ERC Starting Grant TEEMBIO project: http://www.will.chez-alice.fr/Research.html

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