PolicyEngine Analysis

Patterns for creating policy impact analyses, dashboards, and research using PolicyEngine.

For Users 👥

What are Analysis Repositories?

Analysis repositories produce the research you see on PolicyEngine:

Blog posts:

• "How Montana's tax cuts affect poverty"
• "Harris EITC proposal costs and impacts"
• "UK Budget 2024 analysis"

Dashboards:

• State tax comparisons
• Policy proposal scorecards
• Interactive calculators (GiveCalc, SALT calculator)

Research reports:

• Distributional analyses for organizations
• Policy briefs for legislators
• Impact assessments

How Analysis Works

1. Define policy reform using PolicyEngine parameters
2. Create household examples showing specific impacts
3. Run population simulations for aggregate effects
4. Calculate distributional impacts (who wins, who loses)
5. Create visualizations (charts, tables)
6. Write report following policyengine-writing-skill style
7. Publish to blog or share with stakeholders

Reading PolicyEngine Analysis

Key sections in typical analysis:

The proposal:

• What policy changes
• Specific parameter values

Household impacts:

• 3-5 example households
• Dollar amounts for each
• Charts showing impact across income range

Statewide/national impacts:

• Total cost or revenue
• Winners and losers by income decile
• Poverty and inequality effects

See policyengine-writing-skill for writing conventions.

For Analysts 📊

When to Use This Skill

• Creating policy impact analyses
• Building interactive dashboards with Streamlit/Plotly
• Writing analysis notebooks
• Calculating distributional impacts
• Comparing policy proposals
• Creating visualizations for research
• Publishing policy research

Example Analysis Repositories

• crfb-tob-impacts - Policy impact analyses
• newsletters - Data-driven newsletters
• 2024-election-dashboard - Policy comparison dashboards
• marginal-child - Specialized policy analyses
• givecalc - Charitable giving calculator

Repository Structure

Standard analysis repository structure:

analysis-repo/
├── analysis.ipynb           # Main Jupyter notebook
├── app.py                   # Streamlit app (if applicable)
├── requirements.txt         # Python dependencies
├── README.md               # Documentation
├── data/                   # Data files (if needed)
├── outputs/                # Generated charts, tables
└── .streamlit/             # Streamlit config
    └── config.toml

Common Analysis Patterns

Pattern 1: Impact Analysis Across Income Distribution

import pandas as pd
import numpy as np
from policyengine_us import Simulation

# Define reform
reform = {
    "gov.irs.credits.ctc.amount.base_amount": {
        "2024-01-01.2100-12-31": 5000
    }
}

# Analyze across income distribution
incomes = np.linspace(0, 200000, 101)
results = []

for income in incomes:
    # Baseline
    situation = create_situation(income=income)
    sim_baseline = Simulation(situation=situation)
    tax_baseline = sim_baseline.calculate("income_tax", 2024)[0]

    # Reform
    sim_reform = Simulation(situation=situation, reform=reform)
    tax_reform = sim_reform.calculate("income_tax", 2024)[0]

    results.append({
        "income": income,
        "tax_baseline": tax_baseline,
        "tax_reform": tax_reform,
        "tax_change": tax_reform - tax_baseline
    })

df = pd.DataFrame(results)

Pattern 2: Household-Level Case Studies

# Define representative households
households = {
    "Single, No Children": {
        "income": 40000,
        "num_children": 0,
        "married": False
    },
    "Single Parent, 2 Children": {
        "income": 50000,
        "num_children": 2,
        "married": False
    },
    "Married, 2 Children": {
        "income": 100000,
        "num_children": 2,
        "married": True
    }
}

# Calculate impacts for each
case_studies = {}
for name, params in households.items():
    situation = create_family(**params)

    sim_baseline = Simulation(situation=situation)
    sim_reform = Simulation(situation=situation, reform=reform)

    case_studies[name] = {
        "baseline_tax": sim_baseline.calculate("income_tax", 2024)[0],
        "reform_tax": sim_reform.calculate("income_tax", 2024)[0],
        "ctc_baseline": sim_baseline.calculate("ctc", 2024)[0],
        "ctc_reform": sim_reform.calculate("ctc", 2024)[0]
    }

case_df = pd.DataFrame(case_studies).T

Pattern 3: State-by-State Comparison

states = ["CA", "NY", "TX", "FL", "PA", "OH", "IL", "MI"]

state_results = []
for state in states:
    situation = create_situation(income=75000, state=state)

    sim_baseline = Simulation(situation=situation)
    sim_reform = Simulation(situation=situation, reform=reform)

    state_results.append({
        "state": state,
        "baseline_net_income": sim_baseline.calculate("household_net_income", 2024)[0],
        "reform_net_income": sim_reform.calculate("household_net_income", 2024)[0],
        "change": (sim_reform.calculate("household_net_income", 2024)[0] -
                  sim_baseline.calculate("household_net_income", 2024)[0])
    })

state_df = pd.DataFrame(state_results)

Pattern 4: Marginal Analysis (Winners/Losers)

import plotly.graph_objects as go

# Calculate across income range
situation_with_axes = {
    # ... setup ...
    "axes": [[{
        "name": "employment_income",
        "count": 1001,
        "min": 0,
        "max": 200000,
        "period": 2024
    }]]
}

sim_baseline = Simulation(situation=situation_with_axes)
sim_reform = Simulation(situation=situation_with_axes, reform=reform)

incomes = sim_baseline.calculate("employment_income", 2024)
baseline_net = sim_baseline.calculate("household_net_income", 2024)
reform_net = sim_reform.calculate("household_net_income", 2024)

gains = reform_net - baseline_net

# Identify winners and losers
winners = gains > 0
losers = gains < 0
neutral = gains == 0

print(f"Winners: {winners.sum() / len(gains) * 100:.1f}%")
print(f"Losers: {losers.sum() / len(gains) * 100:.1f}%")
print(f"Neutral: {neutral.sum() / len(gains) * 100:.1f}%")

Visualization Patterns

Standard Plotly Configuration

import plotly.graph_objects as go

# PolicyEngine brand colors
TEAL = "#39C6C0"
BLUE = "#2C6496"
DARK_GRAY = "#616161"

def create_pe_layout(title, xaxis_title, yaxis_title):
    """Create standard PolicyEngine chart layout."""
    return go.Layout(
        title=title,
        xaxis_title=xaxis_title,
        yaxis_title=yaxis_title,
        font=dict(family="Roboto Serif", size=14),
        plot_bgcolor="white",
        hovermode="x unified",
        xaxis=dict(
            showgrid=True,
            gridcolor="lightgray",
            zeroline=True
        ),
        yaxis=dict(
            showgrid=True,
            gridcolor="lightgray",
            zeroline=True
        )
    )

# Use in charts
fig = go.Figure(layout=create_pe_layout(
    "Tax Impact by Income",
    "Income",
    "Tax Change"
))
fig.add_trace(go.Scatter(x=incomes, y=tax_change, line=dict(color=TEAL)))

Common Chart Types

1. Line Chart (Impact by Income)

fig = go.Figure()
fig.add_trace(go.Scatter(
    x=df.income,
    y=df.tax_change,
    mode='lines',
    name='Tax Change',
    line=dict(color=TEAL, width=3)
))
fig.update_layout(
    title="Tax Impact by Income Level",
    xaxis_title="Income",
    yaxis_title="Tax Change ($)",
    xaxis_tickformat="$,.0f",
    yaxis_tickformat="$,.0f"
)

2. Bar Chart (State Comparison)

fig = go.Figure()
fig.add_trace(go.Bar(
    x=state_df.state,
    y=state_df.change,
    marker_color=TEAL
))
fig.update_layout(
    title="Net Income Change by State",
    xaxis_title="State",
    yaxis_title="Change ($)",
    yaxis_tickformat="$,.0f"
)

3. Waterfall Chart (Budget Impact)

fig = go.Figure(go.Waterfall(
    x=["Baseline", "Tax Credit", "Phase-out", "Reform"],
    y=[baseline_revenue, credit_cost, phaseout_revenue, 0],
    measure=["absolute", "relative", "relative", "total"],
    connector={"line": {"color": "gray"}}
))

Streamlit Dashboard Patterns

Basic Streamlit Setup

import streamlit as st
from policyengine_us import Simulation

st.set_page_config(page_title="Policy Analysis", layout="wide")

st.title("Policy Impact Calculator")

# User inputs
col1, col2, col3 = st.columns(3)
with col1:
    income = st.number_input("Income", value=60000, step=5000)
with col2:
    state = st.selectbox("State", ["CA", "NY", "TX", "FL"])
with col3:
    num_children = st.number_input("Children", value=0, min_value=0, max_value=10)

# Calculate
if st.button("Calculate"):
    situation = create_family(
        parent_income=income,
        num_children=num_children,
        state=state
    )

    sim_baseline = Simulation(situation=situation)
    sim_reform = Simulation(situation=situation, reform=reform)

    # Display results
    col1, col2, col3 = st.columns(3)
    with col1:
        st.metric(
            "Baseline Tax",
            f"${sim_baseline.calculate('income_tax', 2024)[0]:,.0f}"
        )
    with col2:
        st.metric(
            "Reform Tax",
            f"${sim_reform.calculate('income_tax', 2024)[0]:,.0f}"
        )
    with col3:
        change = (sim_reform.calculate('income_tax', 2024)[0] -
                 sim_baseline.calculate('income_tax', 2024)[0])
        st.metric("Change", f"${change:,.0f}", delta=f"${-change:,.0f}")

Interactive Chart with Streamlit

# Create chart based on user inputs
incomes = np.linspace(0, income_max, 1001)
results = []

for income in incomes:
    situation = create_situation(income=income, state=selected_state)
    sim = Simulation(situation=situation, reform=reform)
    results.append(sim.calculate("household_net_income", 2024)[0])

fig = go.Figure()
fig.add_trace(go.Scatter(x=incomes, y=results, line=dict(color=TEAL)))
st.plotly_chart(fig, use_container_width=True)

Jupyter Notebook Best Practices

Notebook Structure

# Cell 1: Title and Description
"""
# Policy Analysis: [Policy Name]

**Date:** [Date]
**Author:** [Your Name]

## Summary
Brief description of the analysis and key findings.
"""

# Cell 2: Imports
import pandas as pd
import numpy as np
import plotly.graph_objects as go
from policyengine_us import Simulation

# Cell 3: Configuration
YEAR = 2024
STATES = ["CA", "NY", "TX", "FL"]

# Cell 4+: Analysis sections with markdown headers

Export Results

# Save DataFrame
df.to_csv("outputs/impact_analysis.csv", index=False)

# Save Plotly chart
fig.write_html("outputs/chart.html")
fig.write_image("outputs/chart.png", width=1200, height=600)

# Save summary statistics
summary = {
    "total_winners": winners.sum(),
    "total_losers": losers.sum(),
    "avg_gain": gains[winners].mean(),
    "avg_loss": gains[losers].mean()
}
pd.DataFrame([summary]).to_csv("outputs/summary.csv", index=False)

Repository-Specific Examples

This skill includes example templates in the examples/ directory:

• impact_analysis_template.ipynb - Standard impact analysis
• dashboard_template.py - Streamlit dashboard
• state_comparison.py - State-by-state analysis
• case_studies.py - Household case studies
• reform_definitions.py - Common reform patterns

Common Pitfalls

Pitfall 1: Not Using Consistent Year

Problem: Mixing 2024 and 2025 calculations

Solution: Define year constant at top:

CURRENT_YEAR = 2024
# Use everywhere
simulation.calculate("income_tax", CURRENT_YEAR)

Pitfall 2: Inefficient Simulations

Problem: Creating new simulation for each income level

Solution: Use axes for efficiency:

# SLOW
for income in incomes:
    situation = create_situation(income=income)
    sim = Simulation(situation=situation)
    results.append(sim.calculate("income_tax", 2024)[0])

# FAST
situation_with_axes = create_situation_with_axes(incomes)
sim = Simulation(situation=situation_with_axes)
results = sim.calculate("income_tax", 2024)  # Array of all results

Pitfall 3: Forgetting to Compare Baseline and Reform

Problem: Only showing reform results

Solution: Always show both:

results = {
    "baseline": sim_baseline.calculate("income_tax", 2024),
    "reform": sim_reform.calculate("income_tax", 2024),
    "change": reform - baseline
}

PolicyEngine API Usage

For larger-scale analyses, use the PolicyEngine API:

import requests

def calculate_via_api(situation, reform=None):
    """Calculate using PolicyEngine API."""
    url = "https://api.policyengine.org/us/calculate"

    payload = {
        "household": situation,
        "policy_id": reform_id if reform else baseline_policy_id
    }

    response = requests.post(url, json=payload)
    return response.json()

Testing Analysis Code

import pytest

def test_reform_increases_ctc():
    """Test that reform increases CTC as expected."""
    situation = create_family(income=50000, num_children=2)

    sim_baseline = Simulation(situation=situation)
    sim_reform = Simulation(situation=situation, reform=reform)

    ctc_baseline = sim_baseline.calculate("ctc", 2024)[0]
    ctc_reform = sim_reform.calculate("ctc", 2024)[0]

    assert ctc_reform > ctc_baseline, "Reform should increase CTC"
    assert ctc_reform == 5000 * 2, "CTC should be $5000 per child"

Documentation Standards

README Template

# [Analysis Name]

## Overview
Brief description of the analysis.

## Key Findings
- Finding 1
- Finding 2
- Finding 3

## Methodology
Explanation of approach and data sources.

## How to Run

\```bash
pip install -r requirements.txt
python app.py  # or jupyter notebook analysis.ipynb
\```

## Outputs
- `outputs/chart1.png` - Description
- `outputs/results.csv` - Description

## Contact
PolicyEngine Team - hello@policyengine.org

Additional Resources

• PolicyEngine API Docs: https://policyengine.org/us/api
• Analysis Examples: https://github.com/PolicyEngine/analysis-notebooks
• Streamlit Docs: https://docs.streamlit.io
• Plotly Docs: https://plotly.com/python/