Extend economic uprating parameters to 2100 using SSA Trustees data

[baogorek]

Summary

This PR extends all economic uprating parameters from 2036 through 2100 using data from the Social Security Administration (SSA) Trustees Report 2025, ensuring PolicyEngine US can perform accurate long-term microsimulations through the end of the century.

What Changed

Previously, most uprating parameters only extended to 2035 (CBO projections). This PR adds 65 years of additional projections (2036-2100) for:

✅ Inflation indices

• SSA CPI-W (Social Security COLA)
• IRS CPI-U (tax parameter indexing)

✅ Wage growth

• SSA Average Wage Index (AWI)

✅ Income categories (all aggregate totals)

• Self-employment income
• Interest & ordinary dividends
• Qualified dividends
• Pension income
• Capital gains
• Adjusted Gross Income (AGI)

✅ Demographics

• Total US population projections

---

Methodology

Growth Rate Strategy

All projections use SSA Trustees data for consistency and to leverage their comprehensive 75-year forecasts:

Income Category	Growth Rate	2100 Value	Rationale
Wages	SSA AWI (~3.5%)	$1.03T	Official wage index used for Social Security
Self-employment	SSA GDP (~4.0%)	$30.8T	Business activity tracks overall economy
Interest & ordinary divs	SSA GDP (~4.0%)	$7.3T	Fixed income grows with savings/GDP
Qualified dividends	GDP + 0.5% (~4.5%)	$32.6T	Equity outperformance premium
Pensions	SSA GDP (~4.0%)	$46.8T	Wage growth + demographic trends
Capital gains	GDP + 0.5% (~4.5%)	$61.2T	Asset appreciation tracks equity returns
Population	SSA demographics (+0.37%)	458.3M	Official demographic projections

Key Design Decisions

1. Why SSA Trustees instead of CBO?

• SSA projects through 2100 (vs CBO's 2055)
• More authoritative for Social Security/demographic projections
• Internally consistent across all economic variables

2. Why maintain AGI ratios?

• Each income category maintains its 2035 ratio to AGI
• Preserves economic relationships between income types
• Simplifies long-term projections while remaining realistic

3. Why equity premium for dividends/capital gains?

• Historical data shows equities outperform GDP by ~0.5-1% annually
• More realistic than CBO's 1.74% cap gains growth (which reflects realization timing effects)
• Both income types come from equity ownership → should have similar long-term growth

4. Population growth already in income projections?

• ✅ Yes! GDP growth = Population growth + Productivity + Inflation
• Income aggregates inherently include population via GDP growth
• Population parameter used separately for survey weight adjustments

---

Technical Implementation

Files Modified

Core parameter files:

policyengine_us/parameters/
├── gov/
│   ├── ssa/
│   │   ├── uprating.yaml          # Extended CPI-W to 2100
│   │   └── wage_index.yaml        # NEW: AWI projections to 2100
│   └── irs/
│       └── uprating.yaml          # Extended CPI-U to 2100
└── calibration/gov/
    ├── cbo/
    │   └── income_by_source.yaml  # Extended 6 income categories
    └── census/populations/
        └── total.yaml             # Updated with SSA population data

Source data & documentation:

policyengine_us/uprating_project/
├── Trustees_Highlights.ods        # SSA GDP, CPI-W, AWI data
├── SSPopJul_TR2024.csv           # Population by age (1941-2100)
├── CBO_Long_term.xlsx            # CBO historical comparisons
├── UPRATING_PLAN.md              # Original methodology plan
└── income_uprating_summary.md    # Implementation summary

Example: Self-Employment Income Extension

self_employment_income:
  # ... CBO values through 2035 ...
  2035-01-01: 2_412_400_000_000
  
  # Extended projections (2036-2100) using SSA GDP growth
  # Methodology: Applied SSA GDP growth rates to maintain consistency with AGI
  # Self-employment maintains 9.24% of AGI (2035 ratio)
  2036-01-01: 2_465_540_268_658
  2040-01-01: 2_879_619_127_752
  2050-01-01: 4_237_230_502_324
  2075-01-01: 11_319_967_194_846
  2100-01-01: 30_782_649_357_335

---

Data Sources

Primary Source: SSA Trustees Report 2025

Main report:
https://www.ssa.gov/oact/TR/2025/

Single-year supplementary tables:
https://www.ssa.gov/oact/tr/2025/lrIndex.html

• Contains: GDP, CPI-W, Average Wage Index projections (2025-2100)
• Used for: All economic growth rates

Demographics (2024 latest):
https://www.ssa.gov/oact/HistEst/Population/2024/

• Contains: Population by single year of age (1941-2100)
• Used for: Total US population projections

Supplementary: CBO Long-Term Economic Projections

https://www.cbo.gov/data/budget-economic-data

• See: "Long Term Economic Projections" spreadsheet
• Contains: CPI-U, income category projections (2025-2055)
• Used for: Historical comparisons and validation

---

Validation

Growth Rate Comparison

Rate	CBO (2025-2035)	SSA (2025-2100)	Notes
Nominal GDP	4.37% → 3.42%	~4.0%	SSA slightly higher, more stable
Wages (AWI)	3.74% → 3.29%	~3.5%	Well aligned
CPI-U	~2.3%	~2.3%	Very close
CPI-W	~2.4%	~2.4%	Identical methodology

SSA vs CBO Population

Year	SSA Trustees	CBO	Difference
2025	346.6M	349.8M	-0.9%
2035	367.2M	364.1M	+0.8%
2050	389.7M	371.5M	+4.9%
2100	458.3M	(no data)	-

SSA projects slightly higher long-term population growth than CBO.

---

Impact

Microsimulation Benefits

1. Extended time horizon: Can now simulate tax/benefit policies through 2100
2. Demographic analysis: Enables studies of aging population effects on entitlements
3. Long-term projections: Climate policy, Social Security reforms, etc.
4. Internal consistency: All parameters use same SSA Trustees source

No Breaking Changes

• ✅ All existing parameters (2015-2035) unchanged
• ✅ Only adds future values beyond CBO's 2035 horizon
• ✅ Maintains backward compatibility
• ✅ Existing simulations produce identical results

---

Testing

Validation Performed

• Growth rates match SSA Trustees Report values
• Income ratios to AGI maintained from 2035 baseline
• Population values sum correctly across all age groups
• Equity premium consistently applied to dividend/cap gains
• All YAML files parse correctly
• Values formatted with underscore thousands separators

---

Changelog Entry

- bump: minor
  changes:
    added:
      - Extended economic uprating parameters to 2100 using SSA Trustees Report 2025 data
      - Added SSA Average Wage Index projections through 2100  
      - Extended income category projections (self-employment, dividends, pensions, capital gains)
      - Updated population projections with SSA Trustees demographic data through 2100

---

Future Work

Potential enhancements not included in this PR:

• State-level population projections (currently only national total)
• Age-stratified economic growth rates (currently aggregate)
• Alternative scenarios (low/high growth variants from Trustees)
• Automatic parameter updates when new Trustees reports published

---

Questions?

For detailed methodology, see:

• /policyengine_us/uprating_project/UPRATING_PLAN.md
• /policyengine_us/uprating_project/income_uprating_summary.md

🤖 Generated with Claude Code

Co-Authored-By: Claude [email protected]

[baogorek]

I'm having Claude Code create some new tests.

[PavelMakarchuk]

Some formatting nits and questions

[PavelMakarchuk]

Can we convert all .py tests into .yaml unit tests - will save a lot of computation time when running the full test suite (any PR)

[PavelMakarchuk]

The parameter descriptions are surfaced in the web app. Can we keep it to one sentence and have all of the other information be commented in the file directly

[PavelMakarchuk]

are those relevant changes to this PR? A little nervous about changing anything LSR related in here, would prefer a separate PR

[baogorek]

Max had asked me to merge his PR in a while ago, but perhaps he'd like me to split it out again. I'm going to leave this until Monday and sync with him then to ask.

[PavelMakarchuk]

same description comment