Counterfactual Explanation Algorithms for Behavioral and Textual Data
  We study the interpretability of predictive systems that use high-dimensonal
behavioral and textual data. Examples include predicting product interest based
on online browsing data and detecting spam emails or objectionable web content.
Recently, counterfactual explanations have been proposed for generating insight
into model predictions, which focus on what is relevant to a particular
instance. Conducting a complete search to compute counterfactuals is very
time-consuming because of the huge dimensionality. To our knowledge, for
behavioral and text data, only one model-agnostic heuristic algorithm (SEDC)
for finding counterfactual explanations has been proposed in the literature.
However, there may be better algorithms for finding counterfactuals quickly.
This study aligns the recently proposed Linear Interpretable Model-agnostic
Explainer (LIME) and Shapley Additive Explanations (SHAP) with the notion of
counterfactual explanations, and empirically benchmarks their effectiveness and
efficiency against SEDC using a collection of 13 data sets. Results show that
LIME-Counterfactual (LIME-C) and SHAP-Counterfactual (SHAP-C) have low and
stable computation times, but mostly, they are less efficient than SEDC.
However, for certain instances on certain data sets, SEDC's run time is
comparably large. With regard to effectiveness, LIME-C and SHAP-C find
reasonable, if not always optimal, counterfactual explanations. SHAP-C,
however, seems to have difficulties with highly unbalanced data. Because of its
good overall performance, LIME-C seems to be a favorable alternative to SEDC,
which failed for some nonlinear models to find counterfactuals because of the
particular heuristic search algorithm it uses. A main upshot of this paper is
that there is a good deal of room for further research. For example, we propose
algorithmic adjustments that are direct upshots of the paper's findings.
