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Four-fifths rule

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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
ch. 20, Fairness measures the law recognises
Chapters
ch. 16, Fairness & XAI · ch. 20, Existing Law
Source
1 numbered reference, listed below

Where it is used

3 chapters of the Body of Knowledge use the term. Each link opens the first section that does.

Four-fifths rule: mentions per chapter6 mentions of the term across 3 of the 23 chapters of the Body of Knowledge; the chapters the glossary cross-references are drawn solid.Cross-referenced chapterOther chapter08 Regulatory Map: 1 mention08 Regulatory Map116 Fairness & XAI: 2 mentions16 Fairness & XAI220 Existing Law: 3 mentions20 Existing Law3No mentions in the other 20 chaptersSource: the Body of Knowledgev0.5.0
Four-fifths rule: mentions per chapter6 mentions of the term across 3 of the 23 chapters of the Body of Knowledge; the chapters the glossary cross-references are drawn solid.Cross-referenced chapterOther chapter000102030405060708 Regulatory Map: 1 mention10810111213141516 Fairness & XAI: 2 mentions21617181920 Existing Law: 3 mentions320212223Source: the Body of Knowledge v0.5.0
Mentions per chapter How often each chapter names the term, with the chapters the glossary cross-references drawn solid. The longest bar is where to read the term in use; bars spread across many chapters mark a term that runs through the discipline.
Mentions as a table
Mentions of Four-fifths rule per chapter
ChapterMentionsCross-referenced
00 Preface0No
01 Definition0No
02 Why Now0No
03 Values & Principles0No
04 The Stack0No
05 Patterns0No
06 The Role0No
07 Maturity Model0No
08 Regulatory Map1No
10 Reading List0No
11 AI Defined0No
12 Governance Program0No
13 Risk Management0No
14 Development0No
15 Deployment0No
16 Fairness & XAI2Yes
17 Incidents0No
18 EU AI Act0No
19 Privacy & AI0No
20 Existing Law3Yes
21 AI Laws Worldwide0No
22 Principles & Standards0No
23 AI Agents0No

Patterns that use this term

One pattern page uses the term.

Sources

  1. [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)

Definitions of legal terms paraphrase the cited text, which governs. Dated statements are as of .

Cite this term

García Aibar, J. (2026). Four-fifths rule. In AI Governance Engineering: The Thesis & Body of Knowledge (v0.5.0), Glossary. https://doi.org/10.5281/zenodo.22956197. https://aigovernanceengineer.com/glossary/four-fifths-rule. CC BY 4.0

BibTeX

@misc{aige2026fourfifthsrule,
  author  = {Jorge García Aibar},
  title   = {{Four-fifths rule}},
  note    = {Glossary, AI Governance Engineering: The Thesis \& Body of Knowledge, version 0.5.0},
  year    = {2026},
  doi     = {10.5281/zenodo.22956197},
  url     = {https://aigovernanceengineer.com/glossary/four-fifths-rule}
}