diff --git a/src/microplex_us/pipelines/ecps_replacement_comparison.py b/src/microplex_us/pipelines/ecps_replacement_comparison.py
index ee0b2ad..3853d1d 100644
--- a/src/microplex_us/pipelines/ecps_replacement_comparison.py
+++ b/src/microplex_us/pipelines/ecps_replacement_comparison.py
@@ -258,6 +258,32 @@ def build_sound_ecps_replacement_comparison(
             "holdout_targets": int(holdout_mask.sum()),
             "protected_family_losses": protected_family_losses,
         },
+        "entity_structure": {
+            "candidate_source": _entity_structure_summary(
+                candidate_path,
+                period=period,
+            ),
+            "baseline_source": _entity_structure_summary(
+                baseline_path,
+                period=period,
+            ),
+            "candidate_matched": _entity_structure_summary(
+                matched_candidate_path,
+                period=period,
+            ),
+            "baseline_matched": _entity_structure_summary(
+                matched_baseline_path,
+                period=period,
+            ),
+            "candidate_refit": _entity_structure_summary(
+                candidate_refit_path,
+                period=period,
+            ),
+            "baseline_refit": _entity_structure_summary(
+                baseline_refit_path,
+                period=period,
+            ),
+        },
         "summary": score_summary,
         "score": pe_native_scores,
         "candidate_refit": _strip_weights(candidate_refit),
@@ -338,6 +364,146 @@ def _household_weights(
     return household_ids, weights
 
 
+def _entity_structure_summary(
+    dataset_path: str | Path,
+    *,
+    period: int,
+) -> dict[str, Any]:
+    path = Path(dataset_path).expanduser().resolve()
+    period_key = str(period)
+    with h5py.File(path, "r") as handle:
+        household_ids = _read_period_array(handle, "household_id", period_key)
+        person_ids = _read_period_array(handle, "person_id", period_key)
+        person_household_ids = _read_period_array(
+            handle,
+            "person_household_id",
+            period_key,
+        )
+        if person_ids.shape[0] != person_household_ids.shape[0]:
+            raise ValueError(
+                f"{path} person_id and person_household_id lengths differ"
+            )
+
+        household_count = int(household_ids.shape[0])
+        summary: dict[str, Any] = {
+            "dataset": str(path),
+            "period": int(period),
+            "household_count": household_count,
+            "person_count": int(person_ids.shape[0]),
+        }
+        for entity in ("tax_unit", "spm_unit", "family", "marital_unit"):
+            plural = _ENTITY_PLURALS[entity]
+            entity_summary = _entity_membership_summary(
+                handle,
+                entity=entity,
+                period_key=period_key,
+                person_household_ids=person_household_ids,
+                household_count=household_count,
+                dataset_path=path,
+            )
+            summary[entity] = entity_summary
+            summary[f"{entity}_count"] = entity_summary["unit_count"]
+            summary[f"{plural}_per_household"] = entity_summary["units_per_household"]
+    return summary
+
+
+_ENTITY_PLURALS = {
+    "tax_unit": "tax_units",
+    "spm_unit": "spm_units",
+    "family": "families",
+    "marital_unit": "marital_units",
+}
+
+
+def _read_period_array(
+    handle: h5py.File,
+    variable: str,
+    period_key: str,
+) -> np.ndarray:
+    if variable not in handle or period_key not in handle[variable]:
+        raise ValueError(f"Dataset is missing {variable}/{period_key}")
+    return np.asarray(handle[variable][period_key], dtype=np.int64)
+
+
+def _entity_membership_summary(
+    handle: h5py.File,
+    *,
+    entity: str,
+    period_key: str,
+    person_household_ids: np.ndarray,
+    household_count: int,
+    dataset_path: Path,
+) -> dict[str, Any]:
+    entity_ids = _read_period_array(handle, f"{entity}_id", period_key)
+    person_entity_ids = _read_period_array(
+        handle,
+        f"person_{entity}_id",
+        period_key,
+    )
+    if person_entity_ids.shape[0] != person_household_ids.shape[0]:
+        raise ValueError(
+            f"{dataset_path} person_{entity}_id and person_household_id "
+            "lengths differ"
+        )
+    unique_entity_ids = np.unique(entity_ids)
+    duplicate_unit_id_count = int(entity_ids.shape[0] - unique_entity_ids.shape[0])
+    unique_person_entity_ids, inverse = np.unique(
+        person_entity_ids,
+        return_inverse=True,
+    )
+    member_counts = np.bincount(inverse)
+    singleton_count = int(np.count_nonzero(member_counts == 1))
+    empty_unit_count = int(
+        np.setdiff1d(unique_entity_ids, unique_person_entity_ids).size
+    )
+    missing_referenced_unit_count = int(
+        np.setdiff1d(unique_person_entity_ids, unique_entity_ids).size
+    )
+    cross_household_count = _cross_household_entity_count(
+        inverse,
+        person_household_ids,
+    )
+    unit_count = int(entity_ids.shape[0])
+    return {
+        "unit_count": unit_count,
+        "person_membership_count": int(person_entity_ids.shape[0]),
+        "duplicate_unit_id_count": duplicate_unit_id_count,
+        "units_per_household": (
+            float(unit_count / household_count) if household_count else None
+        ),
+        "singleton_unit_count": singleton_count,
+        "singleton_unit_share": (
+            float(singleton_count / unit_count) if unit_count else None
+        ),
+        "empty_unit_count": empty_unit_count,
+        "missing_referenced_unit_count": missing_referenced_unit_count,
+        "cross_household_unit_count": cross_household_count,
+    }
+
+
+def _cross_household_entity_count(
+    entity_inverse: np.ndarray,
+    person_household_ids: np.ndarray,
+) -> int:
+    if entity_inverse.size == 0:
+        return 0
+    order = np.argsort(entity_inverse, kind="stable")
+    sorted_entity = entity_inverse[order]
+    sorted_household = person_household_ids[order]
+    boundaries = np.concatenate(
+        (
+            np.asarray([0]),
+            np.flatnonzero(np.diff(sorted_entity)) + 1,
+            np.asarray([sorted_entity.size]),
+        )
+    )
+    cross_household_count = 0
+    for start, stop in zip(boundaries[:-1], boundaries[1:], strict=True):
+        if np.unique(sorted_household[start:stop]).size > 1:
+            cross_household_count += 1
+    return cross_household_count
+
+
 def _extract_pe_native_loss_inputs(
     *,
     input_dataset_path: str | Path,
diff --git a/tests/pipelines/test_ecps_replacement_comparison.py b/tests/pipelines/test_ecps_replacement_comparison.py
index 34d5db5..ce3d724 100644
--- a/tests/pipelines/test_ecps_replacement_comparison.py
+++ b/tests/pipelines/test_ecps_replacement_comparison.py
@@ -264,6 +264,20 @@ def test_sound_ecps_replacement_comparison_satisfies_gate_contract(
         "household_net_income",
     }
     assert summary["protected_family_losses"]["wages"]["n_targets"] == 1
+    structure = payload["entity_structure"]["candidate_matched"]
+    assert structure["household_count"] == 2
+    assert structure["person_count"] == 3
+    assert structure["tax_unit_count"] == 2
+    assert structure["tax_unit"]["singleton_unit_count"] == 1
+    assert structure["tax_unit"]["singleton_unit_share"] == pytest.approx(0.5)
+    assert structure["tax_unit"]["duplicate_unit_id_count"] == 0
+    assert structure["tax_unit"]["missing_referenced_unit_count"] == 0
+    assert structure["tax_unit"]["cross_household_unit_count"] == 0
+    assert structure["spm_unit_count"] == 2
+    assert structure["family_count"] == 2
+    assert structure["marital_unit_count"] == 3
+    assert structure["marital_unit"]["singleton_unit_share"] == pytest.approx(1.0)
+    assert payload["entity_structure"]["baseline_refit"]["household_count"] == 2
     candidate_curve = payload["candidate_refit"]["loss_curve"]
     baseline_curve = payload["baseline_refit"]["loss_curve"]
     assert candidate_curve[0]["iteration"] == 0