[R] "prob" in predict(randomForest)

Häring, Tim (LWF) Tim.Haering at lwf.bayern.de
Tue May 5 09:53:42 CEST 2009

Hi at all,

maybe this question is quite simple for a statistician, but for me it is not. After reading a lot of mail in the R-help archive I`m still not quite sure I get it. 
When applying a randomForest to a new dataset with predict(randomForest) I have the option to get the output as probability (classification problem):
I would like to know how I have to understand this output. Are this values the probability of an observation belonging to a predicted class? Say, I have a data-point as newdata, my rf-model predicts Class A and the probability is 0,12301. Does this mean that this data-point belongs to class A only with a probability of 12%?

Thanks for every hint.


Just as a matter of form: I´m using R version 2.8.1, randomForest package 4.5-28, OS: WinXP

Tim Häring
Bavarian State Institute of Forest Research 
Department of Forest Ecology
Am Hochanger 11
D-85354 Freising

E-Mail: tim.haering at lwf.bayern.de

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