reviewing-reidentification-risk

Reviewing re-identification risk

Removing direct identifiers is not enough. A record stripped of name, SSN, and MRN can still be singled out by a combination of quasi-identifiers — age, ZIP/region, admission date, sex, rare diagnosis. The HIPAA Expert Determination pathway (45 CFR 164.514(b)(1)) requires a qualified person to apply statistical methods and document that the risk of re-identification is "very small." This skill produces that evidence: quasi-identifier risk metrics (k-anonymity, l-diversity) plus OpenMed's empirical re-identification attack, written up as a residual-risk memo.

When to use

• After direct-identifier removal passes auditing-deid-leakage (no leaks) and you must decide whether the dataset is releasable.
• The user invokes Expert Determination, asks for a re-identification risk score, k-anonymity, l-diversity, or a "very small risk" determination memo.
• You need an adversarial linkage attack — modeling an attacker with auxiliary data — not just a structural metric.

Quick start

from openmed.eval.attacks.reid import run_reid_attack, run_reid_benchmark

# Synthetic de-identified records; each row is the released, de-id'd data.
deidentified = [
    {"record_id": "r1", "text": "[NAME], 47F, ZIP 021xx, admitted 2024-03."},
    {"record_id": "r2", "text": "[NAME], 47F, ZIP 021xx, admitted 2024-03."},
    {"record_id": "r3", "text": "[NAME], 88M, ZIP 597xx, admitted 2024-03."},  # singleton
]
# Auxiliary = what an attacker might already hold (e.g. a voter list).
auxiliary = [{"record_id": "v9", "text": "88M ZIP 597xx"}]

result = run_reid_attack(
    fixtures=[],                          # bring your own records below
    deidentified_records=deidentified,
    auxiliary_records=auxiliary,
)
metric = result.to_metric()
print(metric["aux_linkage_rate"],        # empirical linkage success
      metric["k_min"],                   # smallest equivalence-class size
      metric["singleton_count"],         # k=1 records (uniquely identifiable)
      metric["quasi_identifier_count"])