Knowing the arithmetic is half the unit. This half is about what the four-fifths result does and does not settle, and what the guidelines require next.
The rule's own caveat
Section 4(D) qualifies itself in both directions, and the exam tests the qualification more than the rule.
- Smaller differences may still constitute adverse impact where they are significant in both statistical and practical terms, or where the employer's actions have discouraged applicants disproportionately.
- Greater differences may not constitute adverse impact where they rest on small numbers that are not statistically significant.
So four-fifths is neither a fixed legal threshold nor a safe harbour. Clearing 80 percent does not make an employer immune from a disparate impact claim. There is no minimum applicant count for the rule to apply.
A ratio of 78 percent built from 9 hires out of 14 applicants and 5 out of 10 is the case in point. Do not halt the process as though the number were conclusive, and do not dismiss it because the pool is small. Analyse the data first, then act.
What counts as a selection procedure
Section 16Q defines a selection procedure as any measure, combination of measures, or procedure used as a basis for any employment decision, expressly naming informal or casual interviews and unscored application forms. "There is no test here" is not an answer. Adverse impact analysis still applies to unstructured interviews and unscored applications.
What follows a finding of impact
Section 3(A): use of a procedure with adverse impact is considered discriminatory and inconsistent with the guidelines unless the procedure has been validated in accordance with the guidelines, or the provisions of section 6 are satisfied.
Notice what is not a defence. Consistent administration to all applicants does not cure impact. Absence of discriminatory intent is irrelevant to an impact analysis. Industry custom is not validation evidence.
Why the highest rate is the denominator
Because section 4(D) frames the rule that way: each group's rate is compared with the rate of the group having the highest rate. Not the largest applicant pool, not the majority workforce group, not census participation rates.
Carry this in: below 80 percent is evidence, and the next step is validation or analysis, never a conclusion.