Re: [R] Random Forest

From: Peter Langfelder <peter.langfelder_at_gmail.com>
Date: Tue, 24 May 2011 16:01:41 -0700

On Tue, May 24, 2011 at 3:18 PM, Unger, Rachel <rachel.unger_at_cahnrs.wsu.edu> wrote:
> I'm analyzing data using Random Forest Regression.  For some of the
> species I am analyzing, the percent variation explained is negative.
> Could you please explain to me what that means?  If you need more
> information, please let me know.  Thank you.

If you're using the rsq component of the randomForest output, negative value means the mean error is larger than the variance of the response y. This could be because the predictor performs really poorly but also because of some calibration issue.

You may want to consult someone face to face to diagnose the problem. As a start, I would look at a scatterplot of observed vs. predicted values to see whether there is a systematic effect

HTH, Peter



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https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide http://www.R-project.org/posting-guide.html and provide commented, minimal, self-contained, reproducible code. Received on Tue 24 May 2011 - 23:10:13 GMT

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