Deid Reid Harness

De-id ⟷ Re-id Adversarial Eval Harness

📊 See RESULTS.md for a verified sample run — the privacy-utility frontier, the cross-track headline (49/50 records vulnerable despite a perfect Safe Harbor scrub), and every figure with a 95% CI — no need to run anything.

The core idea

A de-identifier's real metric is not its recall — it is its survival against the best available re-identification attacker. So the attacker is the eval. Report a scrubber's score only as its survival against a defined attack, never as a standalone "accuracy."

The attacker is really three different attackers, corresponding to three threat models with three different standards. Never collapse them into one number:

1. Direct-identifier leakage → HIPAA Safe Harbor (a checklist: remove 18 identifier categories). Deterministically scorable because ground truth is known.
2. Quasi-identifier linkage → Expert Determination (a statistical argument that re-id risk is very small). Needs a background population as denominator.
3. Free-text inference → the pure AI-era threat (a model derives identity from context that never states it). Needs an LLM judge; the only track where ground truth can't be enumerated.

A Safe Harbor pass can still be an Expert Determination failure. That divergence is the whole point of the harness — surface it, don't hide it.

What this slice builds (Tracks 1 and 2)

Track 1 (Safe Harbor leakage) is implemented end to end first, because it is the only track that is deterministically scorable — you get a working closed loop with trustworthy numbers before touching the harder tracks. Track 2 (Expert Determination) is a statistical-linkage attacker that needs no LLM judge either, the second load-bearing, model-independent scorer. Track 3 (inference) is now built too, with a deterministic, model-independent baseline attacker so it also verifies offline; a real LLM attacker is a documented swap-in that runs through the sibling agent-eval skill. All three tracks share one corpus generator; each attack is a separate scorer.

The closed loops:

generate_corpus.py  ->  run_track1.py  ->  score_leakage.py     (Track 1: Safe Harbor)
   (synthetic notes       (defender runs        (deterministic Safe
    + ground-truth          over corpus)          Harbor coverage,
    manifest; --population                        sliced by cat×form×context)
    and --inference add
    Track 2 & 3 inputs)

generate_corpus.py --population N  ---->  score_reid.py          (Track 2: Expert Det.)
                                             (statistical linkage: k-anonymity +
                                              prosecutor/journalist/marketer risk)

generate_corpus.py --inference  ------->  score_inference.py     (Track 3: inference)
   (diagnosis-free vignettes)                (attacker recovers the withheld
                                              diagnosis; emits agent-eval JSONL)

Running it

cd scripts
# Track 1 — Safe Harbor leakage
python generate_corpus.py --n 50 --seed 20260101 --population 100000 --inference --utility --out corpus.json
python run_track1.py --corpus corpus.json --pipeline regex-baseline-v0 --out runs.jsonl
python score_leakage.py --runs runs.jsonl --out leakage_report.json

# Track 2 — Expert Determination re-id risk (reads population_ref from the corpus)
python score_reid.py --corpus corpus.json --out reid_report.json

# Track 3 — free-text inference (attacker recovers the withheld diagnosis)
python score_inference.py --corpus corpus.json --out inference_report.json --eval-out inference_eval.jsonl
python ../../agent-eval/scripts/score_eval.py inference_eval.jsonl   # optional: aggregate/diff

# Utility axis + privacy-utility frontier (needs a --utility corpus for clinical spans)
python score_utility.py --corpus corpus.json --runs runs.jsonl --leakage-report leakage_report.json
python score_frontier.py --corpus corpus.json --out frontier.json   # (privacy, utility) per defender

# Cross-track synthesis — the punchline (needs --population AND --inference)
python score_crosstrack.py --corpus corpus.json --out crosstrack_report.json

# Statistical rigor — 95% CIs + paired significance test on ONE corpus
python score_stats.py --corpus corpus.json --out stats.json
# ...or a seed sweep across K independently generated corpora
python score_stats.py --seeds 10 --n 50 --out stats_sweep.json

# Regression suite — invariants + verified headline numbers (stdlib only, ~6s)
python test_harness.py

test_harness.py locks the load-bearing invariants (byte-identical corpus across flags, span offset self-tests, redacted-span structure, utility-overlap logic, cross-track ≡ standalone-scorer consistency) and the verified numbers (0.449 baseline, the two frontier corners, 0.94 recovery, 49/50 cross-track). A failure means a result moved — run it before committing changes to the generator or any scorer.

Statistical rigor. Every number above is a point estimate on n=50, one seed — score_stats.py puts a 95% confidence interval on each of them (a cluster bootstrap over records, since a note's spans are correlated, not independent evidence — see references/statistical-rigor.md), and a paired bootstrap test of whether two defenders' privacy/utility genuinely differ on the same records. On the bundled defenders, both frontier gaps are significant at α=0.05. A --seeds K sweep regenerates the corpus across K independent seeds to confirm a result isn't an artifact of one draw: over-redact's privacy (0.886–0.900 across 5 seeds) never overlaps the baseline's (0.417–0.456).

Track 1. The bundled regex-baseline-v0 defender is deliberately weak. On the default corpus it scores ~0.45 Safe Harbor coverage, and the breakdown is the point: ISO dates are caught 100%, but spelled-out and narrative dates 0%, names 0%, and the patient's city and facility code 0%. That is the category × surface_form × context diagnostic working as intended — a single averaged number would have hidden exactly the gaps that matter. The report also lists categories_not_exercised — the Safe Harbor categories the corpus never injects (fax, URL, IP, device IDs, …) — so a coverage number over 8 categories is never mistaken for coverage of the full 18-item checklist.

Track 2. Against a 100k-person background population, every one of the 50 notes is unique on its generalized QIs (age band, sex, ZIP3, rare-diagnosis flag) — so the released cohort is not k-anonymous at any k ≥ 2 (min_k = 1), prosecutor risk is 1.0, and 6 of 50 records are unique even against the full 100,000-person population (mean journalist/marketer risk ≈ 0.37). Read against Track 1, that is the entire thesis in one run: a note whose 18 direct identifiers are perfectly scrubbed (Safe Harbor pass) is still a re-identification target through the QIs that must clinically remain (Expert Determination fail). One caveat the report states in-band: the v0 generator draws ZIP3 uniformly, so the QI space is more dispersed than real geography — the prosecutor / k-anonymity numbers are an upper bound, and the population-side risks are the load-bearing figures. A Synthea-backed population restores realistic class sizes.

Track 3. Each note gets a diagnosis-free vignette rendering the diagnosis's clinical signature; the attacker must name the withheld diagnosis from context alone. The bundled knowledge-only signature-match-v0 attacker recovers it in ~0.94 of cases — 1.0 for rare diagnoses (distinctive signatures leak almost perfectly), 0.93 for common ones — while correctly abstaining on the ~6% of vignettes reduced to non-specific features. These notes carry no direct identifiers (Safe Harbor would pass them) and are not being linked (Track 2's job); the leak is pure inference, which neither other track can see. Scoring is programmatic against the closed diagnosis set, and the scorer emits agent-eval's JSONL schema so a real LLM attacker's free-text guesses can later be graded and calibrated through the agent-eval skill.

Utility axis / frontier. All three tracks measure privacy; the utility axis measures what a defender destroys. --utility marks the clinical spans a good scrubber must keep (diagnosis, age ≤ 89, sex — clinically necessary, non-identifying), and score_frontier.py gives each defender a (privacy, utility) pair. The two bundled defenders sit at opposite corners — regex-baseline-v0 at privacy 0.449 / utility 1.00 (barely redacts) and over-redact-v0 at privacy 0.900 / utility 0.60 (sweeps up names and dates but deletes every age and the capitalized diagnoses). Neither dominates; the gap between them is the frontier, and the whole reason a privacy score is never reported alone.

Cross-track synthesis — the punchline. score_crosstrack.py joins the tracks per record to compute the claim the whole harness exists to make. It assumes the best case for the defender — a perfect Safe Harbor scrub, all 18 direct-identifier categories gone — then asks of each record: still re-identifiable (Track 2, population k < 5) or still inferable (Track 3, diagnosis recovered)? On the default corpus, 49 of 50 records (98%) are re-identifiable or inferable despite being perfectly Safe-Harbor-clean (34 re-id, 47 inferable, 32 both; rare diagnoses 6/6). Those are checklist false-negatives: certified de-identified, and not. It reuses Track 2's linkage and Track 3's attacker directly (per- record outputs verified identical to the standalone scorers), so it is deterministic and adds no new assumptions.

Architecture — swappable parts + your eval harness as orchestrator

Corpus generator (generate_corpus.py). Emits synthetic notes and a manifest whose spans are exact by construction: notes are assembled from segments and each identifier's offset is recorded at placement time, then a self-test asserts note_text[start:end] == text for every span. This is why Track 1 needs no tagger and no judge. The person source is a registry (person_sources.py): synthetic-v0 (default, make_person, byte-identical) or fhir-synthea, which reads Synthea FHIR R4 bundles so real demographics flow through the same injection/manifest machinery (--person-source fhir-synthea --fhir-dir …; see references/data-sources.md). The surface-form layer renders each logical identifier several realistic ways (a date as ISO, slashed, spelled-out, or narrative; a name as initials; identifiers in headers, signatures, and buried in narrative), because real notes leak precisely where they are messy.

De-id pipeline / defender (deid_pipelines.py). A pluggable interface (scrub(text) -> (scrubbed_text, redacted_spans_or_None)) with a registry, so the same eval runs against a regex baseline, a rule-based scrubber, an LLM scrubber, and a hybrid — comparing pipelines on one frontier is the deliverable. Two ship: the weak regex-baseline-v0 (under-redacts) and over-redact-v0 (over-redacts), the two corners of the frontier. A pipeline that reports its redaction spans gets exact scoring; a black-box pipeline returns None and the scorers fall back to surface-string presence checks.

Re-id attackers / scorers (score_leakage.py = Track 1; score_reid.py = Track 2; score_inference.py + inference_attackers.py = Track 3). For Track 1 the attacker is deterministic: did each ground-truth span survive? Output is coverage sliced by category, by category×surface-form, and by context — never averaged into one figure. For Track 2 the attacker is statistical: over the generalized QI equivalence classes it computes k-anonymity and prosecutor/journalist/marketer risk against the background population (qi_model.py holds the one generalization both the population generator and the scorer share). For Track 3 the attacker is a swappable inference engine (registry in inference_attackers.py, like the defenders) that recovers a withheld attribute from context; the bundled baseline is model-independent, and a real LLM attacker is the documented swap-in. All three bundled attackers are model-independent, so none can share a base model with the defender — the harness's cardinal rule holds by construction.

Utility scorer + frontier (score_utility.py, score_frontier.py). The mirror of the Track 1 attacker: instead of "did an identifier survive?" it asks "did clinical content survive?" over the --utility clinical spans, then score_frontier.py pairs each defender's privacy and utility into the frontier point. Deterministic, so it never depends on a model's blind spots.

Orchestrator (run_track1.py, and later your existing agent-eval harness). agent-eval is where the adversarial-eval and judge-calibration machinery plug in: it orchestrates runs, calibrates the inference-track judge and the attacker's confidence (does a claimed-0.9 re-identification mean 90% correct against ground truth?), and diffs across runs so hardening the scrubber shows up as movement on the frontier.

Two rules that keep the harness honest

Always pair privacy with utility. A scrubber that redacts every token has perfect privacy and zero clinical value — so any privacy number reported without a paired utility metric is meaningless. This is now enforced in code: --utility marks the clinical spans a scrubber must keep, score_utility.py measures preservation, and score_frontier.py plots each defender as a (privacy, utility) point. The real deliverable is that frontier across pipelines, not a leaderboard; over-redaction is a measured cost (over-redact-v0 buys privacy 0.45→0.90 by dropping utility 1.0→0.60), not a safe default.

Never let attacker and defender share a base model. If both are the same LLM their blind spots correlate — the attacker misses exactly what the defender missed and the score looks great and means nothing. Use diverse model families, and keep the model-independent attackers (deterministic manifest check for Track 1; statistical linkage for Track 2; knowledge-only signature match for Track 3) load-bearing so the score never depends on one model's blind spots.

Extending the harness

• Statistical rigor — BUILT. bootstrap.py + score_stats.py add cluster-bootstrap CIs and a paired significance test to every headline metric, plus a seed-sweep mode. Extend it toward a real study by growing n well past 50 and reporting effect sizes alongside CIs, not just significance. See references/statistical-rigor.md.
• Cross-track synthesis — BUILT. score_crosstrack.py reports how many records pass Safe Harbor yet stay re-identifiable or inferable. Extend it when a live LLM attacker lands (its recoveries flow straight in) or when Track 2 gets a Synthea population (the re-id axis stops being an upper bound).
• Track 3 (inference) — BUILT (baseline). score_inference.py runs an attacker over the --inference vignettes and scores recovery of the withheld diagnosis, emitting agent-eval JSONL. The bundled signature-match-v0 is model-independent. The real next step here is the LLM attacker + judge: register an LLM attacker in inference_attackers.py (respecting the no-shared-base-model rule) and move scoring to agent-eval's LLM judge for semantic grading of free-text guesses and confidence calibration. See references/inference-threat.md.
• Utility axis / frontier — BUILT. --utility marks clinical spans, score_utility.py scores preservation, and score_frontier.py reports (privacy, utility) per defender over one corpus. Extend it by adding richer clinical content (labs, meds) as clinical spans and more defenders to the registry to fill in the frontier between the two bundled corners.
• Data fidelity — BUILT (reader), pending real data. The fhir-synthea person source reads Synthea FHIR bundles so real demographics enter at the source — this is what turns Track 2's uniform-ZIP3 upper bound into a defensible estimate. Validated against a bundled fixture; point it at real Synthea output and sanity-check the first run. Still open: a FHIR-sourced Track 2 population, and richer clinical content (labs, meds) for the utility axis.

Reference files

• references/manifest-schema.md — the frozen data contract. Read before changing the generator or writing any scorer; every scorer depends on it.
• references/safe-harbor-identifiers.md — the 18 identifier categories as the Track 1 test taxonomy, and where Safe Harbor and Expert Determination diverge.
• references/expert-determination.md — the Track 2 risk model: quasi-identifiers, equivalence classes, k-anonymity, and the three attackers (prosecutor/journalist/ marketer). Read before changing qi_model.py or score_reid.py.
• references/inference-threat.md — the Track 3 contract: inference vs leakage, the withheld-target invariant, programmatic-vs-judged scoring, and how the inference attacker plugs into agent-eval. Read before changing the inference generator or scorer.
• references/utility-and-frontier.md — the utility axis: clinical spans as the mirror of identifier spans, how preservation is scored, and how the privacy-utility frontier is assembled across defenders. Read before changing score_utility.py or score_frontier.py.
• references/data-sources.md — the person-source registry and the Synthea FHIR → person mapping contract. Read before changing person_sources.py or feeding real Synthea data.
• references/statistical-rigor.md — why the bootstrap resamples records (not spans), the bootstrap vs. seed-sweep distinction, and the paired significance test. Read before changing bootstrap.py or score_stats.py, or before citing a number in a writeup.
• references/expert-determination.md — the Track 2 risk model: quasi-identifiers, equivalence classes, k-anonymity, and the three attackers (prosecutor/journalist/ marketer). Read before changing qi_model.py or score_reid.py.

Standard traceability

Track 1 coverage is reported per Safe Harbor identifier category, so every test maps to the specific identifier it exercises — the standard-anchored coverage matrix reviewers and portfolio readers expect. Label Track 1 results as Safe Harbor coverage, never as re-identification risk; conflating them is the exact error this harness exists to expose.