title: What splitting criterion does Random Tree in Weka 3.7.11 use for numerical attributes?
body: <p>I'm using RandomForest from Weka 3.7.11 which in turn is bagging Weka's RandomTree. My input attributes are numerical and the output attribute(label) is also numerical.</p>
  
  <p>When training the RandomTree, K attributes are chosen at random for each node of the tree. Several splits based on those attributes are attempted and the "best" one is chosen. How does Weka determine what split is best in this (numerical) case?</p>
  
  <p>For nominal attributes I believe Weka is using the <a href="http://en.wikipedia.org/wiki/Information_gain_in_decision_trees" rel="nofollow">information gain</a> criterion which is based on conditional entropy.</p>
  
  <pre><code>IG(T|a) = H(T) - H(T|a)
  </code></pre>
  
  <p>Is something similar used for numerical attributes? Maybe differential entropy?</p>