# How to evaluate clustering with ground truth?

arXiv: https://arxiv.org/abs/2606.27061 · HTML: https://mlsanity.com/paper/2606.27061/

## Key facts

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- First posted on arXiv 25 Jun 2026.

## Abstract (arXiv)

External indexes can be used for cluster evaluation when ground truth is available. We review the most common external validity indexes focusing on set-matching-based measures. We recommend centroid index (CI), because it is an intuitive cluster-level measure with an explainable result. If we need a more fine-tuned, point-level measure, there are more choices. Pair-set index (PSI) provides a normalized score which is not biased by cluster sizes. If all points should matter equally, then clustering accuracy (ACC) or any other set-matching measure is suitable.