Backfill HHS SMI parameter with pre-2021 historical values

[hua7450]

Problem

policyengine_us/parameters/gov/hhs/smi/amount.yaml only has SMI values starting from 2021-10-01 (FY2022). This blocks accurate historical microsimulation for state programs that reference HHS SMI for pre-2021 periods.

Why it matters

Several state child care subsidy and LIHEAP programs reference hhs_smi for income-eligibility computation. Some states also freeze the SMI base year administratively. With no pre-2021 SMI data, those frozen-base-year lookups return zero.

Concrete example — Maryland Child Care Scholarship (PR #7889):

• FY2019-2022: 65% of 2018 SMI (frozen 4 years)
• FY2023-2024: 75% of 2021 SMI (frozen 2 years) — ✅ works (2021 data is in)
• FY2025+: 75% of current SMI — ✅ works

The md_ccs_income_eligible formula already parameterizes smi_base_year, but calls to smi(size, state, "2018-10-01", parameters) return zero because no 2018-10-01 entry exists in amount.yaml. Documented as a known limitation in the formula comment.

What to backfill

Add per-state entries for FY2018, FY2019, FY2020, and FY2021 to amount.yaml:

• 2017-10-01 → SMI values from ACF LIHEAP FFY2018 Attachment 1
• 2018-10-01 → SMI values from ACF LIHEAP FFY2019 Attachment 1
• 2019-10-01 → SMI values from ACF LIHEAP FFY2020 Attachment 1
• 2020-10-01 → SMI values from ACF LIHEAP FFY2021 Attachment 1

Sources

HHS Administration for Children & Families publishes the official SMI tables annually for LIHEAP use. Landing pages and direct Attachment 1 PDFs:

FFY	IM landing page	Attachment 1 PDF
FFY2018	LIHEAP-IM-2017-03	im_17_03_liheap_smi_fy18.pdf#page=4
FFY2019	LIHEAP-IM-2018-03	Direct PDF not published — values transcribed from the landing-page Attachment 1 table
FFY2020	LIHEAP-IM-2019-02	comm_liheap_smiimattachment_1_fy2019.pdf#page=1
FFY2021	LIHEAP-IM-2020-02	comm_liheap_im2002smiattachment_fy2021.pdf#page=1

(The existing amount.yaml metadata already lists FFY2022 through FFY2026 sources from the same series.)

Out of scope

This issue is data backfill only — no formula or schema changes. The hhs.smi.amount parameter is breakdown-by-state with period: year; adding earlier per-state date entries should be mechanical.

Related

• Maryland CCS — the frozen-base-year framework that depends on this: policyengine_us/parameters/gov/states/md/msde/ccs/income/smi_base_year.yaml
• Variable that exhibits the issue: md_ccs_income_eligible.py
• Implementation: Backfill HHS SMI parameter with FY2018-FY2021 historical values #8356 (backfills all four years FFY2018–FFY2021 + test cases)