---
title: "Four-fifths rule"
description: "The US Uniform Guidelines rule of thumb that a group selection rate below 80% of the highest group's rate will generally be regarded as evidence of adverse impact, qualified by statistical and…"
canonical: https://aigovernanceengineer.com/glossary/four-fifths-rule
author: "Jorge García Aibar"
license: "CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/)"
doi: https://doi.org/10.5281/zenodo.22956197
version: "0.5.0"
updated: 2026-09-24
---

# Four-fifths rule

The US Uniform Guidelines rule of thumb that a group selection rate below 80% of the highest group's rate will generally be regarded as evidence of adverse impact, qualified by statistical and practical significance [1]. It is not a safe harbour: smaller gaps can still count.

- Developed in: [ch. 16, The four-fifths rule and the adverse-impact ratio](https://aigovernanceengineer.com/bok/fairness-and-explainability#the-four-fifths-rule-and-the-adverse-impact-ratio); [ch. 20, Fairness measures the law recognises](https://aigovernanceengineer.com/bok/existing-law#fairness-measures-the-law-recognises)
- Chapters: [ch. 16, Fairness & XAI](https://aigovernanceengineer.com/bok/fairness-and-explainability) · [ch. 20, Existing Law](https://aigovernanceengineer.com/bok/existing-law)
- In the glossary chapter: https://aigovernanceengineer.com/bok/glossary#t-four-fifths-rule

## Sources

[1] 29 CFR 1607.4(D), Uniform Guidelines on Employee Selection Procedures (1978) (adverse impact and the "four-fifths rule", with statistical-significance and small-numbers caveats; text as of 2026-09-01). eCFR. 2026-09-01. https://www.ecfr.gov/current/title-29/subtitle-B/chapter-XIV/part-1607/section-1607.4 (verified: primary)