Explaining Random Forest Prediction Through Diverse Rulesets

March, 2022

Abstract

Tree-ensemble algorithms, such as random forest, are effective machine learning methods popular for their flexibility, high performance, and robustness to overfitting. However, since multiple learners are combined,they are not as interpretable as a single decision tree. In this work we propose a methodology, called Local Tree eXtractor (LTreeX) which is able to explain the forest prediction for a given test instance with a few diverse rules. Starting from the decision trees generated by a random forest, our method 1) pre-selects a subset of them, 2) creates a vector representation, and 3) eventually clusters such a representation. Each cluster prototype results in a rule that explains the test instance prediction. We test the effectiveness of LTreeX on 71 real-world datasets and we demonstrate the validity of our approach for binary classification, regression, multi-label classification and time-to-event tasks. In all set-ups, we show that our extracted surrogate model manages to approximate the performance of the corresponding ensemble model, while selecting only few trees from the whole forest.We also show that our proposed approach substantially outperforms other explainable methods in terms of predictive performance.