Four-Fifths Rule (80% Rule)

The four-fifths rule is a practical threshold established by the EEOC's Uniform Guidelines on Employee Selection Procedures (1978). To apply the rule, divide the selection rate of each protected group by the selection rate of the group with the highest rate. If any group's ratio falls below 0.80 (80%), there is evidence of adverse impact. While the four-fifths rule is not a legal standard by itself, it serves as an initial screening tool. Courts and regulators use it alongside statistical significance testing to evaluate whether an AI hiring tool creates unlawful discrimination.