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Fairness and Code Smells in Machine Learning

Reviewed by Greg Wilson / 2023-02-26
Keywords: Code Smells, Fairness, Machine Learning

Radioactivity was touted as a wonder cure for a wide range of ailments in the years following its discovery. That didn't go well, but it was many years (and many needless deaths) before people began to use it safely. We are in the same position today: as people rush to apply machine learning to every imaginable domain, it has the potential to do a great deal of harm unless we we learn how to use it responsibly.

So while ML researchers work to find better algorithms, software engineering researchers study ML itself. These two papers are indicative of the kind of work they do. The first finds that the dozens of fairness metrics in the IBM AIF360 toolkit are highly redundant: they can be clustered into groups such that it's only necessary to check one metric from each group. The second paper describes 22 code smells specific to machine learning that can serve as a checklist for code reviews and linting checks to help ensure that what we ship implements the checks and balances it's supposed to.

Suvodeep Majumder, Joymallya Chakraborty, Gina R. Bai, Kathryn T. Stolee, and Tim Menzies. Fair enough: searching for sufficient measures of fairness. 2021. arXiv:2110.13029.

Testing machine learning software for ethical bias has become a pressing current concern. In response, recent research has proposed a plethora of new fairness metrics, for example, the dozens of fairness metrics in the IBM AIF360 toolkit. This raises the question: How can any fairness tool satisfy such a diverse range of goals? While we cannot completely simplify the task of fairness testing, we can certainly reduce the problem. This paper shows that many of those fairness metrics effectively measure the same thing. Based on experiments using seven real-world datasets, we find that (a) 26 classification metrics can be clustered into seven groups, and (b) four dataset metrics can be clustered into three groups. Further, each reduced set may actually predict different things. Hence, it is no longer necessary (or even possible) to satisfy all fairness metrics. In summary, to simplify the fairness testing problem, we recommend the following steps: (1) determine what type of fairness is desirable (and we offer a handful of such types); then (2) lookup those types in our clusters; then (3) just test for one item per cluster.

Haiyin Zhang, Luís Cruz, and Arie van Deursen. Code smells for machine learning applications. In Proceedings of the 1st International Conference on AI Engineering: Software Engineering for AI. ACM, May 2022. doi:10.1145/3522664.3528620.

The popularity of machine learning has wildly expanded in recent years. Machine learning techniques have been heatedly studied in academia and applied in the industry to create business value. However, there is a lack of guidelines for code quality in machine learning applications. In particular, code smells have rarely been studied in this domain. Although machine learning code is usually integrated as a small part of an overarching system, it usually plays an important role in its core functionality. Hence ensuring code quality is quintessential to avoid issues in the long run. This paper proposes and identifies a list of 22 machine learning-specific code smells collected from various sources, including papers, grey literature, GitHub commits, and Stack Overflow posts. We pinpoint each smell with a description of its context, potential issues in the long run, and proposed solutions. In addition, we link them to their respective pipeline stage and the evidence from both academic and grey literature. The code smell catalog helps data scientists and developers produce and maintain high-quality machine learning application code.