A National Disparate-Impact Audit of College Completion Equity

Employment law uses the four-fifths rule to flag selection procedures with outcomes too unequal across groups; higher education has no comparable standard for completion. This study imports the four-fifths (80%) test into a national audit of college completion using IPEDS data (2018–2022). In 2022, 66% of auditable institutions fail it for Black students; the result is stable across 5 years and robust to the threshold, reference group, cohort size and an absolute-gap measure. It concentrates in broad-access institutions, though its low-completion concentration is partly a ratio artefact. The audit is descriptive, not causal, and shows why the choice of fairness metric is itself a policy decision.