Implement Montana State Supplementary Payment (SSP)

[hua7450]

Summary

Implements Montana's State Supplementary Payment (SSP) — supplements federal Supplemental Security Income (SSI) for aged, blind, and disabled recipients living in qualifying personal-care, foster-care, and transitional-living arrangements (rates frozen since 1989).

Closes #8232

Regulatory Authority

• ARM 37.43.101 — Optional State Supplementation purpose and effective date
• ARM 37.43.102(2)(a)–(d) — Individual eligibility (Group 1 + Group 2)
• ARM 37.43.103 — Qualifying living-arrangement codes (G/H/I/J/K)
• ARM 37.43.104 — Payment standards (individual rates)
• MCA 52-1-104(3) — Statutory authority; prohibits payments to category B assisted living
• SSA POMS SI DEN01415.010 — Couple rates (Effective January 1, 1989)
• SSA State Assistance Programs for SSI Recipients, January 2011 — Montana, Tables 1 and 2 (pp. 67–68)

Program Overview

• Administration: SSA-administered, state-funded (Montana DPHHS)
• Funding: State funds
• Categories: Aged, blind, and disabled (children covered — no age gate)
• Current caseload: 968 recipients in January 2011 (32 aged, 11 blind, 616 disabled adults, 309 children); 2010 expenditures $968,186 (SSA State Assistance Programs report, January 2011, Table 2)

Eligibility

Requirement	Source	How Modeled
Must reside in Montana	ARM 37.43.101	defined_for = StateCode.MT
Must be SSI-eligible with low-enough income (covers Group 1 and Group 2)	ARM 37.43.102(2)(a)	uncapped_ssi > 0 (already implies categorical/resource/immigration eligibility plus income test)
Must reside in a qualifying ARM 37.43.103 facility (codes G/H/I/J/K)	ARM 37.43.102(2)(b); ARM 37.43.103	mt_ssp_payment_category != NONE
Federal SSI financial eligibility	ARM 37.43.102(2)(d)	Subsumed by uncapped_ssi > 0
Federal SSI categorical (aged/blind/disabled) eligibility	ARM 37.43.101	Subsumed by SSI chain feeding uncapped_ssi
Federal SSI immigration rules	ARM 37.43.102 (no state-specific provision)	Subsumed by SSI chain
Federal SSI resource limits	SSA 2011 report (Montana)	Subsumed by SSI chain

Departure from default SSP convention: Montana uses uncapped_ssi > 0 rather than ssi > 0 because ARM 37.43.102(2)(a) explicitly extends eligibility to people "who would be eligible to receive federal supplemental security income except for the amount of their income" (Group 2). Gating on ssi > 0 would incorrectly drop Group 2 recipients.

Benefit Amounts (SSA POMS SI DEN01415.010; ARM 37.43.104; SSA 2011 report Montana Table 1)

Tier (ARM 37.43.103 codes)	Individual	Couple TOTAL	Per Spouse
Personal care / group home / community home (G/H/I)	$94.00	$193.00	$96.50
Foster care home (J)	$52.75	$110.50	$55.25
Transitional living services (K)	$26.00	$57.00	$28.50

Source note on couple rates: The couple amounts ($5 uniform bonus over 2× the individual rate) appear in SSA POMS SI DEN01415.010 and the SSA 2011 State Assistance Programs report (Montana Table 1) only — they are NOT codified in ARM 37.43.104. Both administrative sources are cited in parameters/.../amount/couple.yaml.

Couple treatment: Separate couple rate (not 2× individual). Stored as couple TOTAL and divided by 2 per spouse following the Maine SSP pattern. Couple gate fires only when (a) ssi_claim_is_joint, (b) both spouses are mt_ssp_eligible, (c) both share the same mt_ssp_payment_category, and (d) the marital unit has size 2. When the gate fails, each spouse falls back to the individual rate.

COLA: Frozen since 1989. ARM 37.43.104 was last amended in 1988; the same rates appear in the SSA 2011 report and 2024–2025 SSA factsheets. A single 1989-01-01 parameter entry covers all modeled periods.

Not Modeled (by design)

What	Source	Why Excluded
Category B assisted living exclusion	MCA 52-1-104(3)	We don't track the Montana category A vs category B assisted-living licensure distinction at the moment; documented in mt_ssp_eligible.py docstring
$40 personal-needs-allowance minimum	ARM 37.43.104(3)	Institutional payment-flow rule (constrains facility retention, not benefit amount); federal SSI alone always exceeds $40 so the floor never binds
$100 personal-needs-allowance maximum retention	SSA 2011 report (Montana Table 1 footnote)	Same — institutional payment-flow rule, not benefit augmentation
Mandatory minimum supplementation (December 1973 grandfathered cohort)	ARM 37.43.102(1); P.L. 93-66 §§211–212	Closed grandfather cohort; effectively zero modern recipients
20 CFR 416.2040 federal-program-participation ineligibility	ARM 37.43.102(2)(c)	Implicit via SSI chain (is_ssi_eligible)
Federal medical treatment facility passthrough	ARM 37.43.103 (no medical-facility category)	Montana SSP has no Medicaid-facility code; recipients in federal medical treatment facilities are simply not Montana-SSP-eligible
Relative responsibility / recoveries / liens / assignments	SSA 2011 report (Montana)	None per state — nothing to model

Files

policyengine_us/parameters/gov/states/mt/dphhs/ssp/
  amount/individual.yaml
  amount/couple.yaml

policyengine_us/variables/gov/states/mt/dphhs/ssp/
  mt_ssp.py
  mt_ssp_eligible.py
  mt_ssp_individual.py
  mt_ssp_couple_per_spouse.py
  mt_ssp_payment_category.py

policyengine_us/tests/policy/baseline/gov/states/mt/dphhs/ssp/
  integration.yaml          (15 cases)
  edge_cases.yaml           (7 cases)
  mt_ssp_eligible.yaml      (5 cases)
  mt_ssp_individual.yaml    (5 cases)
  mt_ssp_couple_per_spouse.yaml (6 cases)

Plus registry/rollup edits:

• policyengine_us/variables/household/income/spm_unit/spm_unit_benefits.py — added mt_ssp to BENEFITS list
• policyengine_us/parameters/gov/household/household_state_benefits.yaml — added - mt_ssp under both 2023-01-01: and 2024-01-01: blocks
• policyengine_us/programs.yaml — added Montana entry under ssi_state_supplement state_implementations (status: complete, variable: mt_ssp, parameter_prefix: gov.states.mt.dphhs.ssp)
• changelog.d/mt-ssp.added.md

Verification TODO

• Verify individual rates against ARM 37.43.104
• Verify couple rates against SSA POMS SI DEN01415.010 and SSA 2011 report Montana Table 1
• Verify rates current as of 2024–2025 (SSA factsheets confirm freeze since 1989)
• CI passes

Test plan

• 38 YAML tests pass locally across 5 test files (5 + 5 + 6 + 15 + 7)
• CI passes

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 93.68%. Comparing base (623a65c) to head (a371d6a).
⚠️ Report is 131 commits behind head on main.

Additional details and impacted files

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- Coverage   100.00%   93.68%   -6.32%     
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  Files           12        6       -6     
  Lines          173       95      -78     
  Branches         4        2       -2     
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- Hits           173       89      -84     
- Misses           0        6       +6     

Flag	Coverage Δ
unittests	93.68% <100.00%> (-6.32%)	⬇️

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