How does the model make predictions? A systematic literature review on the explainability power of machine learning in healthcare

Background: Medical use cases for machine learning (ML) are growing exponentially. The first hospitals are already using ML systems as decision support systems in their daily routine. At the same time, most ML systems are still opaque and it is not clear how these systems arrive at their predictions.Methods: In this paper, we provide a brief overview of the taxonomy of explainability methods and review popular methods. In addition, we conduct a systematic literature search on PubMed to investigate which explainable artificial intelligence (XAI) methods are used in 450 specific medical supervised ML use cases, how the use of XAI methods has emerged recently, and how the precision of describing ML pipelines has evolved over the past 20 years.Results: A large fraction of publications with ML use cases do not use XAI methods at all to explain ML pre-dictions. However, when XAI methods are used, open-source and model-agnostic explanation methods are more commonly used, with SHapley Additive exPlanations (SHAP) and Gradient Class Activation Mapping (Grad -CAM) for tabular and image data leading the way. ML pipelines have been described in increasing detail and uniformity in recent years. However, the willingness to share data and code has stagnated at about one-quarter.Conclusions: XAI methods are mainly used when their application requires little effort. The homogenization of reports in ML use cases facilitates the comparability of work and should be advanced in the coming years. Experts who can mediate between the worlds of informatics and medicine will become more and more in demand when using ML systems due to the high complexity of the domain.

Automated summary

Background: The use of machine learning in medical applications is growing rapidly, but most ML systems are still opaque in their decision-making process. In this paper, the authors provide an overview of explainability methods in ML and review popular methods. They also conduct a literature search on PubMed to investigate the use of explainable artificial intelligence (XAI) methods in specific medical supervised ML use cases and the evolution of ML pipeline descriptions. Results: Many publications on ML use cases do not employ XAI methods to explain predictions. However, when XAI methods are used, open-source and model-agnostic explanation methods, such as SHAP and Grad-CAM, are commonly utilized for tabular and image data. The level of detail and uniformity in describing ML pipelines has improved in recent years, but the willingness to share data and code remains limited. Conclusions: XAI methods are mainly used in simpler applications. Standardized reporting in ML use cases can enhance comparability and should be promoted further. With the increasing complexity of the domain, experts who bridge the gap between informatics and medicine will be in high demand when using ML systems.