Re: [om-devel] How to find which layers are most important

[Chris Y. <Chr...@io...>]

Hi Alexander,

There are a number of ways to determine variable importance, either directly or indirectly.  

i) Some algorithms lend themselves to direct interpretations of variable importance by examining the log output or model file.  For example, the pca based algorithms such as ENFA or CSM you can examine the variable loadings for each component and the component weightings.  In OM v 1.2 these values are part of the standard log output for the ENFA algorithm.  I'm sure similar things can be done with the model files to extract variable weightings for other algorithms, although I'm not familiar with all of them.

ii) Indirectly we can examine variable importance by a jackknife/bootstrap procedure.  This is implemented in om-desktop as a pre-analysis tool (although its always been a bit flakey for me).  If you start with N variables, this runs your analysis N times but each time with N-1 variables to determine the model performance (i.e. AUC) without each variable in turn.  Additionally you can run N models with just a single input variable each time to see the performance with a single variable (not possible with every algorithm).

iii) Another indirect way to see the impact of a variable is to do variable response curves.  Select some random points (say 1000) drill these into your projected model and the original variable layer.  Doing a x,y plot of variable against model score will show how the model responds to that variable.  If its a flat line then you can say that this variable doesn't appear to influence the model (at least in isolation).

I've promised someone that I'd write a script to manage a jackknife analysis (ii) from the command line.  I'd be happy to pass this on when I've written it.

I hope this is helpful.

- Chris

Dr Chris Yesson
Postdoctoral Researcher
Institute of Zoology
Zoological Society of London
Regent's Park
London NW1 4RY
020 7449 6267
http://www.zsl.org/chrisyesson/
http://eu-fp7-coralfish.net/




-----Original Message-----
From: Alexander Bruy [mailto:ale...@gm...]
Sent: Sun 2011-10-23 10:44 AM
To: openModeller
Subject: [om-devel] How to find which layers are most important
 
Hi all,

is it possible to find which layers from input layers set are
most important for model creation?

For example, is some Windows programs after generating model
I can see which layers have greater weight in determining the
likehood of occurence. Is it possible to get such information with
openModeller?

I use console tools, not openModeller Desktop

Thanks
-- 
Alexander Bruy

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