Age-based disparate impact in a reduction in force — statistical assessment
| To | [Counsel], [Firm] |
| From | Karim Souidi, M.Sc. (Econometrics), NorthLaw.ai |
| Matter | [Plaintiff] v. [Employer] — sample file NL-2026-0000 (ADEA / state analogue) |
| Date | 24 September 2026 |
| Purpose | Settlement and mediation support. Privileged; prepared at the request of counsel. Not prepared for filing or testimony. |
In the March 2025 reduction in force, employees aged 40 and over were selected for layoff at 2.5 times the rate of younger employees (20.3% vs. 8.1%). The gap is 3.6 standard deviations from what a neutral process would produce, well beyond the two-to-three standard deviation threshold courts treat as significant. After adjusting for tenure and department, the odds of selection for the protected group remain about 2.4 times higher (95% CI 1.3 – 4.6).
The employer's likely rebuttal, that selection tracked performance ratings, weakens but does not eliminate the disparity: with ratings included, the adjusted odds ratio falls to 1.8 and its confidence interval crosses one. The dispute therefore turns on whether the ratings themselves are a legitimate, age-neutral criterion. That is a factual and legal question, not a statistical one, and it is where settlement leverage lies for both sides.
Whether selection for the reduction in force was statistically associated with age; whether that association survives adjustment for the factors the employer says it used; and how robust the finding is to the employer's most likely explanation.
The employer's RIF roster as produced in discovery: 412 employees in the affected business unit, 58 selected. Details in Appendix B.
| Group | Employees | Selected | Selection rate |
|---|---|---|---|
| Under 40 | 210 | 17 | 8.1% |
| 40 and over | 202 | 41 | 20.3% |
| Total | 412 | 58 | 14.1% |
Figure 1. Selection rates by age group. The dashed line is the overall rate; a neutral process would produce roughly that rate in both groups.
| Measure | Result | Interpretation |
|---|---|---|
| Selection rate ratio (40+ ÷ under 40) | 2.5 | Protected group selected 2.5× as often |
| Standard deviations from a neutral process | 3.6 | Exceeds the 2–3 SD range cited in Hazelwood and Castaneda |
| Adjusted odds ratio (tenure, department) | 2.4 (1.3 – 4.6) | Disparity persists after legitimate factors |
| Adjusted odds ratio (+ performance rating) | 1.8 (0.9 – 3.7) | Attenuated; interval includes 1 |
Full results, including the four-fifths screen, exact test and sensitivity analyses, are in Appendix A.
Table A1. Full measures of disparity.
| Measure | Result | Basis |
|---|---|---|
| Expected selections, 40+ (neutral process) | 28.4 | Hypergeometric expectation; observed 41 |
| Standard deviation of expectation | 3.53 | Hypergeometric variance |
| Standard deviations from expectation | 3.6 | (41 − 28.4) ÷ 3.53 |
| Two-sided p-value (Fisher's exact) | < 0.001 | Less than 1 in 1,000 under a neutral process |
| Four-fifths rule (retention rate ratio) | 0.87 | 79.7% ÷ 91.9%; passes the 0.80 screen |
| Logistic regression: age 40+ (tenure, department) | OR 2.4 (1.3 – 4.6) | n = 412; robust SE |
| Logistic regression: + performance rating | OR 1.8 (0.9 – 3.7) | n = 408; four missing ratings excluded |
| Rating difference, 40+ vs under 40 | −0.4 points | Adjusted for tenure and department |
A2. Sensitivity. Using age 50 as the cut-off raises the selection-rate ratio to 3.1 and the standard-deviation measure to 4.2. Excluding the two departments closed in their entirety (all employees selected regardless of age) lowers the raw ratio to 2.2 and leaves the significance conclusion unchanged. Results are not sensitive to the handling of the four missing ratings (dropped vs. imputed at department mean).
A3. Method.
Source: employer's RIF roster produced in discovery (Bates [range]). Fields used: date of birth, hire date, department, job level, 2024 performance rating (1–5), selection indicator. Population: 412 salaried employees in the affected business unit as of the RIF date; 58 selected. Four records with missing ratings were retained for unadjusted analyses and excluded from rating-adjusted models. Age computed at the RIF date. No records were excluded for any other reason. Data were supplied by counsel and not independently verified.