What the rule requires
The Uniform Guidelines on Employee Selection Procedures describe adverse impact using selection rates. A selection rate for any race, sex, or ethnic group that is less than four-fifths, or 80 percent, of the highest group's selection rate is generally regarded by federal enforcement agencies as evidence of adverse impact.
The rule applies to users of selection procedures covered by federal equal employment opportunity requirements, including many employers, employment agencies, labor organizations, licensing bodies, and government-related selection systems. It is a screening rule, not a final legal conclusion.
- Selection rate = selected candidates / total candidates in the group.
- Impact ratio = group selection rate / highest selection rate.
- A ratio below 0.80 is a common adverse impact flag.
How to calculate
Suppose 120 applicants in Group A produce 48 hires, so the selection rate is 48 / 120 = 40 percent. Group B has 80 applicants and 20 hires, so its selection rate is 20 / 80 = 25 percent. The highest selection rate is 40 percent.
The impact ratio for Group B is 25 percent / 40 percent = 0.625, or 62.5 percent. Because 62.5 percent is below four-fifths of the highest rate, the result is an adverse impact flag that should be investigated.
What to do with a flag
A four-fifths flag does not prove unlawful discrimination by itself. It tells the employer to examine whether the selection procedure is job related, consistent with business necessity, validated where required, and whether less adverse alternatives are available.
The analysis should also consider sample size and practical significance. Very small groups can create extreme ratios from one or two decisions, while large groups can show meaningful disparities even when the ratio is near 80 percent.
Common mistakes
Do not compare raw hire counts. A group with fewer hires may still have a higher selection rate if it also had fewer applicants. Do not compare every group to the overall average when the rule calls for comparison with the highest selection rate.
Another mistake is using stale or incomplete applicant-flow data. The candidate pool should match the decision point being analyzed, such as those who took a test, passed a screen, or were eligible for promotion.
- Wrong denominator for the decision stage.
- Combining jobs with different selection criteria.
- Ignoring candidates who withdrew before the selection step.
- Treating the 80 percent rule as the only statistical test.
Who needs it
HR, talent acquisition, industrial-organizational psychologists, compliance teams, and employment counsel use adverse impact calculations to monitor hiring and promotion systems. Vendors may also use them when validating assessments or screening tools.
The calculation is especially important before rolling out tests, automated ranking systems, physical ability screens, background criteria, or promotion panels. Early review can identify a problem before it becomes embedded in a high-volume process.
Frequently asked questions
Is the four-fifths rule legally binding by itself?
It is a federal enforcement guideline and screening tool, not a complete legal determination. Courts and agencies may consider statistical significance, practical significance, validation, and business necessity.
Which group is the reference group?
The usual four-fifths calculation compares each group's selection rate with the highest selection rate among the groups being analyzed.
Can there be adverse impact if the ratio is above 80 percent?
Yes. The guidelines recognize that smaller differences can still matter when they are statistically and practically significant or when applicant discouragement is present.
Should I calculate adverse impact at every hiring step?
Often yes, especially when a particular step such as a test or screen may be driving the disparity. The full process and individual components can both matter.