add: diag

paper3_phase5b_icd_sepsis_prevalence.py

@@ -0,0 +1,447 @@
+"""
+ICD-coded sepsis prevalence — inclusion vs exclusion cohort
+═════════════════════════════════════════════════════════════════════════════
+Companion analysis for paper3_phase5b_refined.py.
+
+The Phase 5b cohort SQL (`q_cohort()`) keeps an ICU stay only when ALL of:
+
+    1. sepsis3.sepsis3 = TRUE                  (Sepsis-3 derived flag)
+    2. ICU length-of-stay ≥ 24h                (H_SNAPSHOT)
+    3. sapsii IS NOT NULL AND sapsii ≥ 48      (SAPS-II Q4)
+
+This script computes the prevalence of *explicit* ICD-coded sepsis on:
+    (a) the INCLUSION cohort  — stays that satisfy all three filters,
+    (b) the EXCLUSION cohort  — every other ICU stay in MIMIC-III (fails
+        at least one of the three filters above), and
+    (c) ALL ICU STAYS         — the full mimiciii.icustays universe
+        (= inclusion ∪ exclusion).
+
+Note: stay-level totals partition cleanly (incl + excl = all), but at the
+admission and subject level a single hadm_id / subject can have ICU stays
+in both buckets, so the "all" row is computed via SQL GROUPING SETS rather
+than by summing.
+
+ICD-coded sepsis is evaluated at the hospital-admission level (a stay is
+"ICD-sepsis +" if its parent hadm_id carries any of the codes below):
+
+    - Explicit sepsis (ICD-9):   995.91, 995.92, 785.52
+       (matches paper2_festung_teil3.py SYNDROME_ICDS["sepsis"]["icd_9"])
+
+    - Angus septicemia (ICD-9):  038.*   (any 038-prefixed code)
+
+    - Any of the above (union)
+
+For each cohort × definition combination we report:
+    n positives, prevalence, Wilson 95% CI.
+The inclusion vs exclusion difference is reported with a normal-approx
+95% CI and a Pearson χ² statistic (no scipy dependency).
+
+Usage:
+  python paper3_phase5b_icd_sepsis_prevalence.py
+"""
+
+import json, math, os, sys, time
+
+# Reuse the same env-var contract as paper3_phase5b_refined.py.
+PG_DSN         = os.environ.get("MIMIC_PG_DSN", "dbname=mimic3")
+MIMIC_SCHEMA   = os.environ.get("MIMIC_SCHEMA",  "mimiciii")
+DERIVED_SCHEMA = os.environ.get("DERIVED_SCHEMA", MIMIC_SCHEMA)
+
+H_SNAPSHOT  = 24      # ICU LOS threshold, hours (matches paper3 phase 5b)
+SAPSII_MIN  = 48      # SAPS-II Q4 cutoff (matches paper3 phase 5b)
+OUT_FILE    = "paper3_phase5b_icd_sepsis_prevalence.json"
+
+# Explicit sepsis codes (ICD-9, MIMIC-III stores them WITHOUT decimal point):
+#   995.91  →  '99591'   Sepsis
+#   995.92  →  '99592'   Severe sepsis
+#   785.52  →  '78552'   Septic shock
+EXPLICIT_SEPSIS_ICD9 = ("99591", "99592", "78552")
+
+# Angus-style broad septicemia bucket: any ICD-9 starting with 038.
+SEPTICEMIA_PREFIX = "038"
+
+
+_PG_CONN = None
+def _pg_conn():
+    global _PG_CONN
+    if _PG_CONN is None or getattr(_PG_CONN, "closed", 0):
+        import psycopg2
+        _PG_CONN = psycopg2.connect(PG_DSN)
+        _PG_CONN.set_session(readonly=True, autocommit=True)
+    return _PG_CONN
+
+
+def run_pg(sql, label=""):
+    import psycopg2.extras
+    conn = _pg_conn()
+    t0 = time.time()
+    with conn.cursor(cursor_factory=psycopg2.extras.RealDictCursor) as cur:
+        cur.execute(sql)
+        rows = [dict(r) for r in cur.fetchall()] if cur.description else []
+    print(f"    {label:40s}  {len(rows):>8,d} rows  ({time.time()-t0:.1f}s)")
+    return rows
+
+
+# ── SQL ─────────────────────────────────────────────────────────────────────
+#
+# One pass: classify every ICU stay as "inclusion" or "exclusion" using the
+# Phase 5b filter, then left-join the two ICD code sets at the hadm_id level
+# and aggregate. This mirrors q_cohort() exactly for the inclusion bucket
+# (sepsis3 = TRUE AND LOS ≥ 24h AND sapsii ≥ 48), and treats every other
+# ICU stay in mimiciii.icustays as exclusion. GROUPING SETS adds a third
+# row (cohort = NULL → 'all') aggregated over the full ICU universe so that
+# admission- and subject-level distinct counts are correct (a single hadm_id
+# may straddle both buckets, so we cannot just sum incl + excl).
+
+def q_prevalence():
+    explicit = ",".join(f"'{c}'" for c in EXPLICIT_SEPSIS_ICD9)
+    return f"""
+WITH icu AS (
+    SELECT icu.icustay_id,
+           icu.hadm_id,
+           icu.subject_id,
+           EXTRACT(EPOCH FROM (icu.outtime - icu.intime)) / 3600.0 AS los_h,
+           COALESCE(s3.sepsis3, FALSE) AS is_sepsis3,
+           saps.sapsii AS sapsii
+      FROM {MIMIC_SCHEMA}.icustays icu
+      LEFT JOIN {DERIVED_SCHEMA}.sepsis3 s3   ON s3.icustay_id   = icu.icustay_id
+      LEFT JOIN {DERIVED_SCHEMA}.sapsii  saps ON saps.icustay_id = icu.icustay_id
+     WHERE icu.icustay_id IS NOT NULL
+       AND icu.hadm_id    IS NOT NULL
+),
+classified AS (
+    SELECT icustay_id, hadm_id, subject_id,
+           is_sepsis3, los_h, sapsii,
+           CASE WHEN is_sepsis3 = TRUE
+                     AND los_h  >= {H_SNAPSHOT}
+                     AND sapsii IS NOT NULL
+                     AND sapsii >= {SAPSII_MIN}
+                THEN 'inclusion' ELSE 'exclusion' END AS cohort
+      FROM icu
+),
+explicit_sepsis AS (
+    SELECT DISTINCT hadm_id
+      FROM {MIMIC_SCHEMA}.diagnoses_icd
+     WHERE icd9_code IN ({explicit})
+),
+septicemia AS (
+    SELECT DISTINCT hadm_id
+      FROM {MIMIC_SCHEMA}.diagnoses_icd
+     WHERE icd9_code LIKE '{SEPTICEMIA_PREFIX}%%'
+)
+SELECT
+    COALESCE(c.cohort, 'all')                   AS cohort,
+    COUNT(*)                                    AS n_stays,
+    COUNT(DISTINCT c.hadm_id)                   AS n_admissions,
+    COUNT(DISTINCT c.subject_id)                AS n_subjects,
+
+    SUM(CASE WHEN e.hadm_id IS NOT NULL
+             THEN 1 ELSE 0 END)                 AS n_stays_explicit,
+    COUNT(DISTINCT CASE WHEN e.hadm_id IS NOT NULL
+                        THEN c.hadm_id END)     AS n_adm_explicit,
+
+    SUM(CASE WHEN s.hadm_id IS NOT NULL
+             THEN 1 ELSE 0 END)                 AS n_stays_septicemia,
+    COUNT(DISTINCT CASE WHEN s.hadm_id IS NOT NULL
+                        THEN c.hadm_id END)     AS n_adm_septicemia,
+
+    SUM(CASE WHEN e.hadm_id IS NOT NULL
+              OR s.hadm_id IS NOT NULL
+             THEN 1 ELSE 0 END)                 AS n_stays_any,
+    COUNT(DISTINCT CASE WHEN e.hadm_id IS NOT NULL
+                          OR s.hadm_id IS NOT NULL
+                        THEN c.hadm_id END)     AS n_adm_any
+  FROM classified c
+  LEFT JOIN explicit_sepsis e ON e.hadm_id = c.hadm_id
+  LEFT JOIN septicemia      s ON s.hadm_id = c.hadm_id
+ GROUP BY GROUPING SETS ((c.cohort), ())
+"""
+
+
+def q_exclusion_breakdown():
+    """How many excluded stays fail each individual filter (non-exclusive
+    counts; an excluded stay can violate >1 criterion)."""
+    return f"""
+WITH icu AS (
+    SELECT icu.icustay_id,
+           EXTRACT(EPOCH FROM (icu.outtime - icu.intime)) / 3600.0 AS los_h,
+           COALESCE(s3.sepsis3, FALSE) AS is_sepsis3,
+           saps.sapsii AS sapsii
+      FROM {MIMIC_SCHEMA}.icustays icu
+      LEFT JOIN {DERIVED_SCHEMA}.sepsis3 s3   ON s3.icustay_id   = icu.icustay_id
+      LEFT JOIN {DERIVED_SCHEMA}.sapsii  saps ON saps.icustay_id = icu.icustay_id
+     WHERE icu.icustay_id IS NOT NULL
+       AND icu.hadm_id    IS NOT NULL
+)
+SELECT
+    COUNT(*)                                                AS n_total,
+    SUM(CASE WHEN is_sepsis3 = FALSE
+             THEN 1 ELSE 0 END)                             AS n_not_sepsis3,
+    SUM(CASE WHEN los_h < {H_SNAPSHOT}
+             THEN 1 ELSE 0 END)                             AS n_los_short,
+    SUM(CASE WHEN sapsii IS NULL
+             THEN 1 ELSE 0 END)                             AS n_sapsii_null,
+    SUM(CASE WHEN sapsii IS NOT NULL AND sapsii < {SAPSII_MIN}
+             THEN 1 ELSE 0 END)                             AS n_sapsii_below
+  FROM icu
+"""
+
+
+def q_icd_sepsis_waterfall():
+    """Mutually-exclusive waterfall, restricted to ICD-coded sepsis stays
+    only, showing which inclusion gate eliminated them.  Uses the union
+    definition (explicit sepsis codes ∪ 038.* septicemia)."""
+    explicit = ",".join(f"'{c}'" for c in EXPLICIT_SEPSIS_ICD9)
+    return f"""
+WITH icu AS (
+    SELECT icu.icustay_id, icu.hadm_id,
+           EXTRACT(EPOCH FROM (icu.outtime - icu.intime)) / 3600.0 AS los_h,
+           COALESCE(s3.sepsis3, FALSE) AS is_sepsis3,
+           saps.sapsii AS sapsii
+      FROM {MIMIC_SCHEMA}.icustays icu
+      LEFT JOIN {DERIVED_SCHEMA}.sepsis3 s3   ON s3.icustay_id   = icu.icustay_id
+      LEFT JOIN {DERIVED_SCHEMA}.sapsii  saps ON saps.icustay_id = icu.icustay_id
+     WHERE icu.icustay_id IS NOT NULL
+       AND icu.hadm_id    IS NOT NULL
+),
+icd_pos AS (
+    SELECT DISTINCT hadm_id
+      FROM {MIMIC_SCHEMA}.diagnoses_icd
+     WHERE icd9_code IN ({explicit})
+        OR icd9_code LIKE '{SEPTICEMIA_PREFIX}%%'
+),
+icd_stays AS (
+    SELECT i.* FROM icu i JOIN icd_pos x ON x.hadm_id = i.hadm_id
+)
+SELECT
+    COUNT(*)                                                  AS n_total_stays,
+    COUNT(DISTINCT hadm_id)                                   AS n_total_adm,
+
+    -- Waterfall: each stay is counted exactly once, in the order of the
+    -- inclusion filter (sepsis3 → LOS → sapsii NULL → sapsii < 48 → pass).
+    SUM(CASE WHEN NOT is_sepsis3
+             THEN 1 ELSE 0 END)                               AS n_fail_sepsis3,
+    SUM(CASE WHEN is_sepsis3 AND los_h < {H_SNAPSHOT}
+             THEN 1 ELSE 0 END)                               AS n_fail_los,
+    SUM(CASE WHEN is_sepsis3 AND los_h >= {H_SNAPSHOT}
+                              AND sapsii IS NULL
+             THEN 1 ELSE 0 END)                               AS n_fail_sapsii_null,
+    SUM(CASE WHEN is_sepsis3 AND los_h >= {H_SNAPSHOT}
+                              AND sapsii IS NOT NULL
+                              AND sapsii < {SAPSII_MIN}
+             THEN 1 ELSE 0 END)                               AS n_fail_sapsii_below,
+    SUM(CASE WHEN is_sepsis3 AND los_h >= {H_SNAPSHOT}
+                              AND sapsii IS NOT NULL
+                              AND sapsii >= {SAPSII_MIN}
+             THEN 1 ELSE 0 END)                               AS n_pass
+  FROM icd_stays
+"""
+
+
+# ── Stats helpers (no scipy) ────────────────────────────────────────────────
+def wilson_ci(k, n, z=1.959963984540054):
+    """Wilson score 95% CI for a binomial proportion. Returns (lo, hi)."""
+    if n <= 0:
+        return (float("nan"), float("nan"))
+    p = k / n
+    denom = 1.0 + z*z/n
+    centre = (p + z*z/(2.0*n)) / denom
+    half   = (z * math.sqrt(p*(1.0 - p)/n + z*z/(4.0*n*n))) / denom
+    return (max(0.0, centre - half), min(1.0, centre + half))
+
+
+def diff_ci(k1, n1, k2, n2, z=1.959963984540054):
+    """Normal-approx 95% CI for (p1 − p2). Returns (delta, lo, hi)."""
+    if n1 <= 0 or n2 <= 0:
+        return (float("nan"),) * 3
+    p1, p2 = k1 / n1, k2 / n2
+    se = math.sqrt(p1*(1.0 - p1)/n1 + p2*(1.0 - p2)/n2)
+    d  = p1 - p2
+    return (d, d - z*se, d + z*se)
+
+
+def chi2_2x2(k1, n1, k2, n2):
+    """Pearson χ² for the 2×2 table (sepsis± × cohort). Returns (chi2, dof=1).
+    Critical value at p=0.05 is 3.841."""
+    a, b = k1, n1 - k1            # incl: sepsis+, sepsis−
+    c, d = k2, n2 - k2            # excl: sepsis+, sepsis−
+    n = n1 + n2
+    if n == 0: return (float("nan"), 1)
+    row1, row2 = a + b, c + d
+    col1, col2 = a + c, b + d
+    chi2 = 0.0
+    for obs, r, col in ((a, row1, col1), (b, row1, col2),
+                         (c, row2, col1), (d, row2, col2)):
+        exp = r * col / n
+        if exp > 0:
+            chi2 += (obs - exp) ** 2 / exp
+    return (chi2, 1)
+
+
+def fmt_pct(p):    return f"{100.0*p:5.2f}%"
+def fmt_ci(lo,hi): return f"[{100.0*lo:5.2f}, {100.0*hi:5.2f}]"
+
+
+# ── Main ────────────────────────────────────────────────────────────────────
+def main():
+    print("\n" + "█"*78)
+    print("  ICD-coded sepsis prevalence — Phase 5b inclusion vs exclusion")
+    print("█"*78)
+    print(f"\n  PG DSN:         {PG_DSN}")
+    print(f"  MIMIC schema:   {MIMIC_SCHEMA}")
+    print(f"  Derived schema: {DERIVED_SCHEMA}")
+    print(f"  Inclusion:      sepsis3=TRUE AND LOS≥{H_SNAPSHOT}h AND SAPS-II≥{SAPSII_MIN}")
+    print(f"  Explicit ICD-9: {', '.join(EXPLICIT_SEPSIS_ICD9)} "
+          f"(995.91 / 995.92 / 785.52)")
+    print(f"  Septicemia:     ICD-9 {SEPTICEMIA_PREFIX}.*")
+
+    print(f"\n[1] Querying MIMIC-III...")
+    rows  = run_pg(q_prevalence(),            "cohort × ICD prevalence")
+    bkdwn = run_pg(q_exclusion_breakdown(),   "exclusion breakdown")
+    wfall = run_pg(q_icd_sepsis_waterfall(),  "ICD-sepsis waterfall")
+
+    if not rows:
+        print("\n[ERROR] no rows returned. Check PG_DSN / schema permissions.")
+        sys.exit(1)
+
+    by = {r["cohort"]: r for r in rows}
+    incl = by.get("inclusion", {})
+    excl = by.get("exclusion", {})
+    allc = by.get("all",       {})
+
+    INT_KEYS = ("n_stays","n_admissions","n_subjects",
+                "n_stays_explicit","n_adm_explicit",
+                "n_stays_septicemia","n_adm_septicemia",
+                "n_stays_any","n_adm_any")
+    for c in (incl, excl, allc):
+        for k in INT_KEYS:
+            c[k] = int(c.get(k) or 0)
+
+    COHORTS = (("inclusion", incl), ("exclusion", excl), ("all", allc))
+
+    # ── [2] Cohort sizes ──────────────────────────────────────────────────
+    print(f"\n[2] Cohort sizes")
+    print(f"    {'cohort':12s}  {'stays':>8s}  {'admissions':>11s}  {'subjects':>9s}")
+    for label, c in COHORTS:
+        print(f"    {label:12s}  {c['n_stays']:>8,d}  "
+              f"{c['n_admissions']:>11,d}  {c['n_subjects']:>9,d}")
+
+    # ── [3] Why an ICU stay was excluded ──────────────────────────────────
+    if bkdwn:
+        b = bkdwn[0]
+        print(f"\n[3] Exclusion breakdown (non-exclusive: a stay can fail >1 filter)")
+        n_total = int(b['n_total'] or 0)
+        for lbl, k in (("not Sepsis-3",          "n_not_sepsis3"),
+                       (f"ICU LOS < {H_SNAPSHOT}h",  "n_los_short"),
+                       ("SAPS-II is NULL",       "n_sapsii_null"),
+                       (f"SAPS-II < {SAPSII_MIN}",   "n_sapsii_below")):
+            n = int(b[k] or 0)
+            pct = 100.0*n/n_total if n_total else 0.0
+            print(f"    {lbl:24s}  {n:>8,d}  ({pct:5.2f}% of all ICU stays)")
+        print(f"    {'all ICU stays':24s}  {n_total:>8,d}")
+
+    # ── [3b] ICD-sepsis-positive waterfall ────────────────────────────────
+    # Diagnostic: of the ICD-coded sepsis stays (explicit ∪ 038.*), which
+    # inclusion gate eliminated them?  Mutually exclusive: each stay is
+    # counted in the FIRST gate that would reject it, walking in the
+    # inclusion-filter order (sepsis3 → LOS → SAPS-II NULL → SAPS-II<48).
+    if wfall:
+        w = wfall[0]
+        n_w = int(w["n_total_stays"] or 0)
+        n_adm = int(w["n_total_adm"]   or 0)
+        print(f"\n[3b] ICD-sepsis-positive waterfall (mutually exclusive,"
+              f" inclusion-filter order)")
+        print(f"     {'gate':28s}  {'n stays':>9s}  {'pct':>6s}  cumulative")
+        cum = 0
+        steps = (
+            ("rejected: not Sepsis-3",      "n_fail_sepsis3"),
+            (f"rejected: LOS < {H_SNAPSHOT}h",  "n_fail_los"),
+            ("rejected: SAPS-II is NULL",   "n_fail_sapsii_null"),
+            (f"rejected: SAPS-II < {SAPSII_MIN}",  "n_fail_sapsii_below"),
+            (f"PASS (= inclusion)",         "n_pass"),
+        )
+        for lbl, kn in steps:
+            n = int(w[kn] or 0)
+            cum += n
+            pct = 100.0*n/n_w if n_w else 0.0
+            print(f"     {lbl:28s}  {n:>9,d}  {pct:5.2f}%  {cum:>9,d}")
+        print(f"     {'TOTAL ICD-sepsis stays':28s}  {n_w:>9,d}  "
+              f"({n_adm:,} admissions)")
+
+    # ── [4] Prevalence per definition ─────────────────────────────────────
+    DEFS = (
+        ("Explicit sepsis (995.91 / 995.92 / 785.52)",
+         "n_stays_explicit",   "n_adm_explicit"),
+        ("Angus septicemia (038.*)",
+         "n_stays_septicemia", "n_adm_septicemia"),
+        ("Any of the above (union)",
+         "n_stays_any",        "n_adm_any"),
+    )
+
+    def _table(title, denom_key_n, denom_key_k):
+        """Render the prevalence table for one denominator (stays or
+        admissions) and append rows to `results[bucket]`."""
+        print(f"\n{title}")
+        print(f"    {'definition':45s}  {'cohort':10s}  "
+              f"{'n+':>7s}  {'N':>7s}  {'prev':>7s}  {'95% CI (Wilson)':>18s}")
+        out = []
+        for name, sk, ak in DEFS:
+            kkey = sk if denom_key_k == "n_stays" else ak
+            for label, c in COHORTS:
+                k_, n_ = c[kkey], c[denom_key_n]
+                p = k_/n_ if n_ else float("nan")
+                lo, hi = wilson_ci(k_, n_)
+                print(f"    {name:45s}  {label:10s}  "
+                      f"{k_:>7,d}  {n_:>7,d}  {fmt_pct(p):>7s}  "
+                      f"{fmt_ci(lo,hi):>18s}")
+                out.append({"definition": name, "cohort": label,
+                            "k": k_, "n": n_, "prevalence": p,
+                            "ci_lo": lo, "ci_hi": hi})
+
+            # Inclusion vs exclusion comparison (the "all" row is just a
+            # weighted average of the two so a Δ against it isn't meaningful).
+            k1, n1 = incl[kkey], incl[denom_key_n]
+            k2, n2 = excl[kkey], excl[denom_key_n]
+            d, dlo, dhi = diff_ci(k1, n1, k2, n2)
+            chi2, dof  = chi2_2x2(k1, n1, k2, n2)
+            sig = "p<0.05" if chi2 > 3.841 else "n.s."
+            print(f"    {'  Δ (incl − excl)':45s}  {'':10s}  "
+                  f"{'':>7s}  {'':>7s}  {fmt_pct(d):>7s}  "
+                  f"{fmt_ci(dlo,dhi):>18s}   χ²={chi2:6.2f} ({sig})")
+            out.append({"definition": name, "cohort": "delta_incl_minus_excl",
+                        "delta": d, "ci_lo": dlo, "ci_hi": dhi,
+                        "chi2": chi2, "dof": dof})
+        return out
+
+    results = {
+        "by_stays":      _table("[4] ICD-coded sepsis prevalence (denominator = ICU STAYS)",
+                                "n_stays", "n_stays"),
+        "by_admissions": _table("[5] ICD-coded sepsis prevalence (denominator = ADMISSIONS)",
+                                "n_admissions", "n_admissions"),
+    }
+
+    # ── Save ────────────────────────────────────────────────────────────
+    output = {
+        "filters": {
+            "h_snapshot_hours": H_SNAPSHOT,
+            "sapsii_min": SAPSII_MIN,
+            "explicit_icd9": list(EXPLICIT_SEPSIS_ICD9),
+            "septicemia_prefix": SEPTICEMIA_PREFIX,
+        },
+        "cohorts": {
+            "inclusion": {k: incl[k] for k in INT_KEYS},
+            "exclusion": {k: excl[k] for k in INT_KEYS},
+            "all":       {k: allc[k] for k in INT_KEYS},
+        },
+        "exclusion_breakdown":      (bkdwn[0] if bkdwn else None),
+        "icd_sepsis_waterfall":     (wfall[0] if wfall else None),
+        "results": results,
+    }
+    with open(OUT_FILE, "w") as f:
+        json.dump(output, f, indent=2, default=str)
+    print(f"\n  → Saved: {OUT_FILE}")
+    print("\n" + "█"*78 + "\n")
+
+
+if __name__ == "__main__":
+    main()

paper3_phase5b_refined.py

@@ -308,18 +308,21 @@ def bedside_score(p):
 
 def build_matrix(ids, primitives, cohort):
     import numpy as np
-    X, y, scores, valid = [], [], [], []
+    X, y, scores, saps, valid = [], [], [], [], []
     for sid in ids:
         p = primitives.get(sid)
         if p is None: continue
         f = formula_features(p)
         s, _ = bedside_score(p)
         if f is None or s is None: continue
+        sap = cohort[sid].get("sapsii")
+        if sap is None: continue
         X.append(f)
         y.append(int(cohort[sid].get("died") or 0))
         scores.append(s)
+        saps.append(float(sap))
         valid.append(sid)
-    return np.array(X), np.array(y), np.array(scores), valid
+    return np.array(X), np.array(y), np.array(scores), np.array(saps), valid
 
 
 # ── Main ────────────────────────────────────────────────────────────────────
@@ -353,8 +356,10 @@ def main():
                and formula_features(primitives[s]) is not None]
     print(f"    usable: {len(all_ids):,}")
 
-    X_all, y_all, S_all, _ = build_matrix(all_ids, primitives, cohort)
+    X_all, y_all, S_all, SAPS_all, _ = build_matrix(all_ids, primitives, cohort)
     print(f"    mortality: {100*y_all.mean():.1f}%")
+    print(f"    SAPS-II:   mean={SAPS_all.mean():.1f}  "
+          f"min={SAPS_all.min():.0f}  max={SAPS_all.max():.0f}")
 
     # ══════════════════════════════════════════════════════════════════════
     # [4] 5-fold CV — 5-term formula
@@ -366,13 +371,13 @@ def main():
     subj_arr = np.array(subject_ids)
     kf = KFold(n_splits=N_FOLDS, shuffle=False)
 
-    fold_aucs, fold_aucs_score, fold_coefs = [], [], []
+    fold_aucs, fold_aucs_score, fold_aucs_saps, fold_coefs = [], [], [], []
     for k, (tr_idx, te_idx) in enumerate(kf.split(subj_arr)):
         tr_subs = set(subj_arr[tr_idx].tolist())
         tr_ids = [s for s in all_ids if cohort[s]["subject_id"] in tr_subs]
         te_ids = [s for s in all_ids if cohort[s]["subject_id"] not in tr_subs]
-        X_tr, y_tr, S_tr, _ = build_matrix(tr_ids, primitives, cohort)
-        X_te, y_te, S_te, _ = build_matrix(te_ids, primitives, cohort)
+        X_tr, y_tr, S_tr, _, _ = build_matrix(tr_ids, primitives, cohort)
+        X_te, y_te, S_te, SAPS_te, _ = build_matrix(te_ids, primitives, cohort)
 
         mu = X_tr.mean(0); sd = X_tr.std(0) + 1e-9
         lr = LogisticRegression(C=1.0, max_iter=1000, random_state=42)
@@ -380,20 +385,35 @@ def main():
         pred = lr.predict_proba((X_te - mu) / sd)[:, 1]
         auc_f = roc_auc_score(y_te, pred)
         auc_s = roc_auc_score(y_te, S_te)        # Ordinal score AUROC
+        auc_saps = roc_auc_score(y_te, SAPS_te)  # SAPS-II baseline AUROC
 
         raw_beta = lr.coef_[0] / sd
         raw_int  = lr.intercept_[0] - sum(lr.coef_[0][i]*mu[i]/sd[i] for i in range(len(sd)))
         fold_aucs.append(auc_f)
         fold_aucs_score.append(auc_s)
+        fold_aucs_saps.append(auc_saps)
         fold_coefs.append([raw_int] + list(raw_beta))
-        print(f"    fold {k+1}: formula AUROC={auc_f:.4f}  ordinal score AUROC={auc_s:.4f}")
+        print(f"    fold {k+1}: formula AUROC={auc_f:.4f}  "
+              f"ordinal AUROC={auc_s:.4f}  SAPS-II AUROC={auc_saps:.4f}")
 
     fa = np.array(fold_aucs); fas = np.array(fold_aucs_score)
+    fsap = np.array(fold_aucs_saps)
     print(f"\n    5-term formula CV AUROC:  {fa.mean():.4f} ± {fa.std():.4f}  "
           f"(range {fa.min():.4f}–{fa.max():.4f})")
     print(f"    Ordinal score  CV AUROC:  {fas.mean():.4f} ± {fas.std():.4f}  "
           f"(range {fas.min():.4f}–{fas.max():.4f})")
+    print(f"    SAPS-II        CV AUROC:  {fsap.mean():.4f} ± {fsap.std():.4f}  "
+          f"(range {fsap.min():.4f}–{fsap.max():.4f})")
     print(f"    Ordinal loss:             {fa.mean()-fas.mean():+.4f}")
+    print(f"    Δ vs SAPS-II (formula):   {fa.mean()-fsap.mean():+.4f}")
+    print(f"    Δ vs SAPS-II (ordinal):   {fas.mean()-fsap.mean():+.4f}")
+
+    # SAPS-II is a fixed pre-computed score (no parameters fit here), so an
+    # in-cohort AUROC is not optimistic — report it on the full Kepler cohort
+    # for a single, directly comparable headline number.
+    saps_auc_overall = roc_auc_score(y_all, SAPS_all)
+    print(f"\n    SAPS-II AUROC on full Kepler cohort (n={len(y_all):,}): "
+          f"{saps_auc_overall:.4f}")
 
     fc = np.array(fold_coefs)
     print(f"\n    Coefficient stability (5 terms):")
@@ -500,8 +520,8 @@ def main():
     tr_subs = set(subs[:n_tr])
     tr_ids = [s for s in all_ids if cohort[s]["subject_id"] in tr_subs]
     te_ids = [s for s in all_ids if cohort[s]["subject_id"] not in tr_subs]
-    X_tr, y_tr, _, _ = build_matrix(tr_ids, primitives, cohort)
-    X_te, y_te, S_te, _ = build_matrix(te_ids, primitives, cohort)
+    X_tr, y_tr, _, _, _ = build_matrix(tr_ids, primitives, cohort)
+    X_te, y_te, S_te, _, _ = build_matrix(te_ids, primitives, cohort)
     mu = X_tr.mean(0); sd = X_tr.std(0) + 1e-9
     lr_cal = LogisticRegression(C=1.0, max_iter=1000, random_state=42)
     lr_cal.fit((X_tr - mu) / sd, y_tr)
@@ -543,6 +563,11 @@ def main():
     print(f"\n    Ordinal bedside score (0–13 pts):")
     print(f"      5-fold CV AUROC:  {fas.mean():.4f} ± {fas.std():.4f}")
     print(f"      AUROC loss vs continuous: {fa.mean()-fas.mean():+.4f}")
+    print(f"\n    SAPS-II baseline (same cohort):")
+    print(f"      Overall AUROC:    {saps_auc_overall:.4f}")
+    print(f"      5-fold CV AUROC:  {fsap.mean():.4f} ± {fsap.std():.4f}")
+    print(f"      Δ formula − SAPS-II: {fa.mean()-fsap.mean():+.4f}")
+    print(f"      Δ ordinal − SAPS-II: {fas.mean()-fsap.mean():+.4f}")
     print(f"\n    Risk bands (ordinal score):")
     for bn in ["low", "mid", "high"]:
         br = band_results.get(bn, {})
@@ -571,6 +596,18 @@ def main():
             "score_distribution": score_rows,
             "risk_bands": band_results,
         },
+        "sapsii_baseline": {
+            "n": int(len(SAPS_all)),
+            "sapsii_mean": float(SAPS_all.mean()),
+            "sapsii_min": float(SAPS_all.min()),
+            "sapsii_max": float(SAPS_all.max()),
+            "auroc_overall": float(saps_auc_overall),
+            "cv_auroc_mean": float(fsap.mean()),
+            "cv_auroc_std": float(fsap.std()),
+            "cv_auroc_range": [float(fsap.min()), float(fsap.max())],
+            "delta_formula_minus_sapsii": float(fa.mean() - fsap.mean()),
+            "delta_ordinal_minus_sapsii": float(fas.mean() - fsap.mean()),
+        },
     }
     with open(OUT_FILE, "w") as f:
         json.dump(output, f, indent=2, default=str)