How can I choose an explainer? An Application-grounded Evaluation of
  Post-hoc Explanations
  There have been several research works proposing new Explainable AI (XAI)
methods designed to generate model explanations having specific properties, or
desiderata, such as fidelity, robustness, or human-interpretability. However,
explanations are seldom evaluated based on their true practical impact on
decision-making tasks. Without that assessment, explanations might be chosen
that, in fact, hurt the overall performance of the combined system of ML model
+ end-users. This study aims to bridge this gap by proposing XAI Test, an
application-grounded evaluation methodology tailored to isolate the impact of
providing the end-user with different levels of information. We conducted an
experiment following XAI Test to evaluate three popular post-hoc explanation
methods -- LIME, SHAP, and TreeInterpreter -- on a real-world fraud detection
task, with real data, a deployed ML model, and fraud analysts. During the
experiment, we gradually increased the information provided to the fraud
analysts in three stages: Data Only, i.e., just transaction data without access
to model score nor explanations, Data + ML Model Score, and Data + ML Model
Score + Explanations. Using strong statistical analysis, we show that, in
general, these popular explainers have a worse impact than desired. Some of the
conclusion highlights include: i) showing Data Only results in the highest
decision accuracy and the slowest decision time among all variants tested, ii)
all the explainers improve accuracy over the Data + ML Model Score variant but
still result in lower accuracy when compared with Data Only; iii) LIME was the
least preferred by users, probably due to its substantially lower variability
of explanations from case to case.
