Pooled ASEC 2022/2023 vintages lack the NOW_* coverage recodes: reported Medicaid at interview thins to 24.6M vs ~58M survey under 65 on the certified artifact

[MaxGhenis]

Summary

On the certified default artifact (hf://policyengine/populace-us/populace_us_2024.h5@populace-us-2024-buildp-sparse-rmloss100-cae8640-20260728T011454Z), the reported-coverage person input has_medicaid_health_coverage_at_interview sums to 24.6M weighted under-65 persons versus ~57.5M survey-reported (CPS ASEC 2023 NOW_MCAID, MARSUPWT). Root cause: the pooled support spine stacks ASEC survey vintages 2022/2023/2024, and the 2022 and 2023 per-year raw H5 inputs never carried the NOW_* at-interview coverage recodes (except NOW_GRP and NOW_MRK). The CPS-carried derivation maps missing/NaN source values to False, so roughly two-thirds of the weighted population — every 2022- and 2023-vintage person, 173.2M weighted under 65 — is structurally unable to report Medicaid (or TRICARE, VA, CHAMPVA, IHS, other-means-tested, or non-marketplace direct-purchase) coverage.

has_esi and has_marketplace_health_coverage_at_interview escape only because NOW_GRP and NOW_MRK happen to be the two NOW_* columns the archived raw-lane converter carried for all vintages.

Downstream consequence (policyengine-scorecard PR #69, annotation kff-medicaid-reported-denominator-sanity): the "no reported coverage" construct identifies 80.9M under-65 persons versus 25.9M survey uninsured-at-interview (NOW_COV==2, ASEC 2023) and ~27M ACS nonelderly uninsured, so uninsured-population constructs on the certified artifact are not survey-faithful. Modeled enrollment is separately CMS-calibrated and does not backfill the reported flag.

No artifacts were published or promoted as part of this investigation.

Reproduction

Weighted person counts on the certified artifact (person-table columns × household weight; the columns are physically present in the h5 and the engine surface reads them as-is), against full-file CPS ASEC 2023 (MARSUPWT/100):

input (under 65, millions)	artifact	ASEC 2023 survey	survey column
has_esi	146.9	164.7	NOW_GRP
has_marketplace_health_coverage_at_interview	21.4	11.4	NOW_MRK
has_non_marketplace_direct_purchase_…_at_interview	4.0	8.8	NOW_NONM
has_medicaid_health_coverage_at_interview	24.6	57.5	NOW_MCAID
has_champva_health_coverage_at_interview	0.3	0.4	NOW_CHAMPVA
has_tricare_health_coverage_at_interview	3.5	6.0	NOW_MIL
has_va_health_coverage_at_interview	0.7	1.6	NOW_VACARE
has_other_means_tested_…_at_interview	0.5	0.7	NOW_OTHMT
has_indian_health_service_coverage_at_interview	0.3	0.8	NOW_IHSFLG
none of the nine ("no reported coverage")	80.9	25.9	NOW_COV==2

The marketplace flag tracks NOW_MRK one-to-one on all vintages, so its level above the ASEC 2023 survey reflects vintage composition and calibration-era weighting, not the missing-column mechanism (out of scope here).

Artifact totals: 340.1M persons, 278.9M under 65 (57,240 households, 166,321 person rows; pe-us pin 1.764.6 per the build manifest).

Compact repro (certified snapshot cached locally)

import os, h5py, numpy as np
p = "~/.cache/huggingface/hub/datasets--policyengine--populace-us/snapshots/26dcad66867687f15735dc4926523e3741920836/populace_us_2024.h5"
f = h5py.File(os.path.expanduser(p), "r")
per, hh = f["person/table"][:], f["household/table"][:]
hw = dict(zip(hh["household_id"], hh["household_weight"]))
w = np.array([hw[h] for h in per["person_household_id"]])
u65 = per["A_AGE"] < 65
flag = per["has_medicaid_health_coverage_at_interview"].astype(bool)
print(w[flag & u65].sum() / 1e6)          # 24.6
for yr in (2022, 2023, 2024):             # vintage split
    m = per["source_year"] == yr
    print(yr, w[m & flag & u65].sum() / 1e6, np.isnan(per["NOW_MCAID"][m]).mean())
# 2022  0.0  1.00 / 2023  0.0  1.00 / 2024  24.6  0.00

Root cause

1. The pooled spine stacks three ASEC survey vintages. source_year on the certified person table: 2022 (54,464 rows, 106.8M weighted), 2023 (54,654 rows, 105.7M), 2024 (57,203 rows, 127.6M). Pooling unions per-year columns via pd.concat (asec_pool.py#L141), leaving NaN where a vintage lacks a column.

2. The 2022/2023 raw H5 inputs lack the NOW_* coverage block. On the certified frame, NOW_MCAID, NOW_CAID, NOW_COV, NOW_MRKS, NOW_MRKUN, NOW_PCHIP, NOW_CHAMPVA, NOW_VACARE, NOW_MIL, NOW_IHSFLG, NOW_NONM, NOW_OTHMT, NOW_PUB, NOW_PRIV, NOW_DIR are populated on exactly the 57,203 2024-vintage rows and NaN on all 109,118 rows from 2022/2023. Only NOW_GRP and NOW_MRK are populated for all vintages. This matches the archived raw-lane converter: policyengine-us-data/datasets/cps/census_cps.py carries NOW_GRP and NOW_MRK in its person column list, and NOW_MCAID never appears anywhere in that file's git history (git log -S NOW_MCAID is empty); the 2024-vintage input was produced by a newer extraction that includes the full block. The input-coverage manifest already documents this vintage asymmetry for other fields ("The 2022 and 2023 inputs also omit PECOHAB, A_EXPRRP, and A_FAMREL; only 2024 carries those alternatives" — is_unmarried_partner_of_household_head exclusion; same pattern in the employer_sponsored_insurance_premiums exclusion, Track SPM-specific input gaps: housing, WIC, school meals, child support, workers comp, and expense deductions #32).

3. The CPS-carried derivation silently maps missing to False. _fill_health_coverage_inputs maps has_medicaid_health_coverage_at_interview ← NOW_MCAID (L272) through _yes_code, where _source returns zeros for an absent column and fillna(0.0) for NaN. The certified flag equals NOW_MCAID == 1 exactly (weighted crosstab: 24.6M both-true, 0.0M in either disagreement cell) — no later stage rewrites it, and the export carries it (this is not the Sparse-57k export drops 94 no-formula input columns from the dense parent (tips, overtime, disability flags, ESI premiums, rent, QBI basis) #361 export-drop class; the column is present).

4. The 2024-vintage slice is survey-plausible; selection and reweighting are not the drivers. Within the 2024 vintage the flag carries 24.6M of 105.7M under-65 = 23.3%, versus 21.1% in full ASEC 2023 (57.5M of 272.7M). Joining the frame's distinct retained ASEC-2023 source persons back to pppub23.csv by PERIDNUM: they capture 9.50% of full-survey under-65 population mass, 9.41% of NOW_MCAID mass, and 9.62% of NOW_GRP mass (original MARSUPWT) — household selection is coverage-neutral. If all three vintages carried the recodes at survey rates, the artifact would report ≈ 0.211 × 278.9M ≈ 59M under-65, consistent with the survey.

5. The Medicaid take-up stage consumes the already-thinned anchor. medicaid_take_up.py anchors on the flag (eligible reporters always take up) and hard-fails only if the column is absent (L173-L177) — there is no guard on per-vintage coverage. The CMS state-count fill compensates in enrollment terms, so enrollment-side calibration passes while the reported-coverage denominator stays thinned; the thinned anchor also shifts enrollment composition from reported toward filled and overstates saturation pressure (Add Medicaid and CHIP eligibility-to-enrollment diagnostics #170's diagnostic direction).

Why certification passed

• release_input_coverage requires the column to be present with non-default signal ("Column mass parity is not column coverage" — the gate closes the absence class, Build J: full eCPS-exported-column coverage as a HARD release gate + asset-column restoration (SSI reforms score $0) #368); 24.6M true satisfies it.
• degenerate_input_signal (175 columns) passes any column that is neither all-default nor constant.
• health_input_signal checks 2 columns (selected_marketplace_plan_benchmark_ratio, takes_up_aca_if_eligible) — no reported-coverage flags.
• ecps_parity is a populated-layer presence check (158 layers, 0 gaps).

Nothing measures per-vintage signal or survey-mass fidelity for the reported-coverage family, so a flag populated for one of three vintages certifies.

Relationship to existing issues

• Pool default-value holes: engine-consumed input leaves with checkpoint sources the pool never populates (is_tanf_enrolled, strike_benefits, receives_medicaid/snap/wic) #591 (pool default-value holes): same family — engine inputs the pool under-populates. Its table notes the sibling receives_medicaid is never emitted while has_medicaid_health_coverage_at_interview "is emitted"; this issue sharpens that: it is emitted for the 2024 vintage only. Partial-vintage holes are invisible to presence-style checks.
• Sparse-57k export drops 94 no-formula input columns from the dense parent (tips, overtime, disability flags, ESI premiums, rent, QBI basis) #361 / Sparse-57k certified release zeroes untargeted input bases (IRA/HSA/SE-pension/childcare); CDCC and ALD reforms silently score ~$0 on bundle 4.18.8 #278 / Sparse-57k certified release drops SSI asset input columns; SSI resource-test reforms score $0 on bundle 4.18.8 #356 (export-side column drops): distinct mechanism — here the column survives export; the values were born thinned at source pooling.
• Ingest ASEC 2024 and 2025 into the US support pool (spine is two vintages behind) #296 (ingest ASEC 2024/2025 into the support pool): the natural vehicle for the data-side fix — any re-extraction should carry the full NOW_* coverage block for every vintage.
• Add Medicaid and CHIP eligibility-to-enrollment diagnostics #170 / Materialize Medicaid and CHIP take-up via anchored count-calibration (ACA stage pattern) #331 / Health take-up wiring + certified-stack computability gate (real residuals from #604) #605 (Medicaid take-up and enrollment diagnostics): enrollment-side consumers of the thinned anchor.
• Add coverage-universe targets for uninsured and private coverage #230 (coverage-universe targets for uninsured and private coverage): targeting the uninsured universe would have surfaced this earlier and remains the calibration-side complement.

Proposed fix

1. Data side (the actual fix): re-extract the 2022 and 2023 per-year raw ASEC H5s with the full NOW_* at-interview coverage block and rebuild the pooled source base. The raw CSVs carry the data — verified for ASEC 2023 (pppub23.csv has NOW_MCAID, column 547); confirm ASEC 2022 at re-extraction. This runs in the gated data lane outside PR CI; no artifact publication is part of this issue.
2. Regression guard (small, PR-able now): a per-vintage reported-coverage signal gate — for each pooled source_year, every reported-coverage input must carry non-default signal (the crisp invariant violated today: 2022/2023 vintages have exactly zero true mass for seven of the nine flags). Ships red against current bases by design, like the Build J: full eCPS-exported-column coverage as a HARD release gate + asset-column restoration (SSI reforms score $0) #368 asset gates, and turns green with the re-extraction.
3. Scorecard follow-up: once a fixed artifact certifies, the kff-medicaid-reported-denominator-sanity annotation and the reported-uninsured rows in policyengine-scorecard PR Target latest eligible Ledger fiscal facts #69 can be revisited.

Numbers computed 2026-08-18 on the locally cached certified snapshot (26dcad668676…, sha256 48b9d479fb4f…) and asecpub23csv with policyengine-us 1.764.6 (the build pin).