SOMtime the World Ain$'$t Fair: Violating Fairness Using Self-Organizing Maps

TL;DR

This paper reveals that unsupervised representations, specifically those produced by Self-Organizing Maps, can inadvertently encode sensitive attributes like age and income, challenging the assumption of neutrality and highlighting the need for fairness auditing beyond supervised tasks.

Contribution

It demonstrates that high-capacity unsupervised models like SOMtime can recover sensitive attribute information, showing that fairness through unawareness fails at the representation level.

Findings

SOMtime recovers monotonic orderings of sensitive attributes with high correlation (up to 0.85).

Unsupervised segmentation produces demographically skewed clusters.

Traditional dimensionality reduction methods show lower correlation with sensitive attributes.

Abstract

Unsupervised representations are widely assumed to be neutral with respect to sensitive attributes when those attributes are withheld from training. We show that this assumption is false. Using SOMtime, a topology-preserving representation method based on high-capacity Self-Organizing Maps, we demonstrate that sensitive attributes such as age and income emerge as dominant latent axes in purely unsupervised embeddings, even when explicitly excluded from the input. On two large-scale real-world datasets (the World Values Survey across five countries and the Census-Income dataset), SOMtime recovers monotonic orderings aligned with withheld sensitive attributes, achieving Spearman correlations of up to 0.85, whereas PCA and UMAP typically remain below 0.23 (with a single exception reaching 0.31), and against t-SNE and autoencoders which achieve at most 0.34. Furthermore, unsupervised segmentation of SOMtime embeddings produces demographically skewed clusters, demonstrating downstream fairness risks without any supervised task. These findings establish that \textit{fairness through unawareness} fails at the representation level for ordinal sensitive attributes and that fairness auditing must extend to unsupervised components of machine learning pipelines. We have made the code available at~ https://github.com/JosephBingham/SOMtime