Towards Enhanced Local Explainability of Random Forests: a
  Proximity-Based Approach
Joshua Rosaler Dhruv Desai Bhaskarjit Sarmah Dimitrios Vamvourellis Deran Onay Dhagash Mehta Stefano Pasquali
We initiate a novel approach to explain the out of sample performance of
random forest (RF) models by exploiting the fact that any RF can be formulated
as an adaptive weighted K nearest-neighbors model. Specifically, we use the
proximity between points in the feature space learned by the RF to re-write
random forest predictions exactly as a weighted average of the target labels of
training data points. This linearity facilitates a local notion of
explainability of RF predictions that generates attributions for any model
prediction across observations in the training set, and thereby complements
established methods like SHAP, which instead generates attributions for a model
prediction across dimensions of the feature space. We demonstrate this approach
in the context of a bond pricing model trained on US corporate bond trades, and
compare our approach to various existing approaches to model explainability.