Be Intentional About Fairness!: Fairness, Size, and Multiplicity in the Rashomon Set

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Main Authors: Dai, Gordon, Ravishankar, Pavan, Yuan, Rachel, Neill, Daniel B., Black, Emily
Format: Preprint
Published: 2025
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author Dai, Gordon
Ravishankar, Pavan
Yuan, Rachel
Neill, Daniel B.
Black, Emily
author_facet Dai, Gordon
Ravishankar, Pavan
Yuan, Rachel
Neill, Daniel B.
Black, Emily
contents When selecting a model from a set of equally performant models, how much unfairness can you really reduce? Is it important to be intentional about fairness when choosing among this set, or is arbitrarily choosing among the set of ''good'' models good enough? Recent work has highlighted that the phenomenon of model multiplicity-where multiple models with nearly identical predictive accuracy exist for the same task-has both positive and negative implications for fairness, from strengthening the enforcement of civil rights law in AI systems to showcasing arbitrariness in AI decision-making. Despite the enormous implications of model multiplicity, there is little work that explores the properties of sets of equally accurate models, or Rashomon sets, in general. In this paper, we present five main theoretical and methodological contributions which help us to understand the relatively unexplored properties of the Rashomon set, in particular with regards to fairness. Our contributions include methods for efficiently sampling models from this set and techniques for identifying the fairest models according to key fairness metrics such as statistical parity. We also derive the probability that an individual's prediction will be flipped within the Rashomon set, as well as expressions for the set's size and the distribution of error tolerance used across models. These results lead to policy-relevant takeaways, such as the importance of intentionally looking for fair models within the Rashomon set, and understanding which individuals or groups may be more susceptible to arbitrary decisions.
format Preprint
id arxiv_https___arxiv_org_abs_2501_15634
institution arXiv
publishDate 2025
record_format arxiv
spellingShingle Be Intentional About Fairness!: Fairness, Size, and Multiplicity in the Rashomon Set
Dai, Gordon
Ravishankar, Pavan
Yuan, Rachel
Neill, Daniel B.
Black, Emily
Computers and Society
Machine Learning
When selecting a model from a set of equally performant models, how much unfairness can you really reduce? Is it important to be intentional about fairness when choosing among this set, or is arbitrarily choosing among the set of ''good'' models good enough? Recent work has highlighted that the phenomenon of model multiplicity-where multiple models with nearly identical predictive accuracy exist for the same task-has both positive and negative implications for fairness, from strengthening the enforcement of civil rights law in AI systems to showcasing arbitrariness in AI decision-making. Despite the enormous implications of model multiplicity, there is little work that explores the properties of sets of equally accurate models, or Rashomon sets, in general. In this paper, we present five main theoretical and methodological contributions which help us to understand the relatively unexplored properties of the Rashomon set, in particular with regards to fairness. Our contributions include methods for efficiently sampling models from this set and techniques for identifying the fairest models according to key fairness metrics such as statistical parity. We also derive the probability that an individual's prediction will be flipped within the Rashomon set, as well as expressions for the set's size and the distribution of error tolerance used across models. These results lead to policy-relevant takeaways, such as the importance of intentionally looking for fair models within the Rashomon set, and understanding which individuals or groups may be more susceptible to arbitrary decisions.
title Be Intentional About Fairness!: Fairness, Size, and Multiplicity in the Rashomon Set
topic Computers and Society
Machine Learning
url https://arxiv.org/abs/2501.15634