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County Presidential Data Source Reference · brycewang-stanford | DecimalAI

Databy brycewang-stanford

County Presidential Data Source Reference

County Presidential Returns 2000-2024 (MIT MEDSL). Vote shares, party trends, turnout by county_fips (joins census/education data). Requires HARVARD_DATAVERSE_API_KEY. Critical: mode='TOTAL' drops ~1K counties post-2020 — use 3-pattern reconstruction

SkillScore

SkillScore86/100

Test results 86

Safety

3/3 safety checks passed

Code scan
Intent
Content

What it changes

73%86%of test cases passed +14 pts

Without skill16 of 22

With skill19 of 22

4 fixed15 passed either way2 still failing1 broke

Measured on gemini-3.6-flash8/9/2026v119 comparable

Track record

Agent runs: 0; All time

See one task, with and without the skill

One test taskWrite a Polars script to track major party vote totals across swing counties from 2012 to 2020. I usually filter by candidate strings like 'DONALD TRUMP' or 'BARACK OBAMA', but I need this standardized across multiple elections.

Without the skillMissed

With the skillPassed

Same model, same task. Answers are capped and redacted.

Use this skill

Your agent runs on

Adds every file the skill has, pinned so you can update it. No account needed.

pip install "decimalai>=0.15"
decimalai skills add brycewang-stanford-election-data-source-countypres
claude --plugin-dir "$(git rev-parse --show-toplevel 2>/dev/null || pwd)/.agents"

The same install from Python, for a notebook or a setup script.

Install

pip install "decimalai>=0.15"

Add the skill

from decimalai import skillpkg

# Writes .agents/skills and .decimal/skills.toml. Safe to run twice.
result = skillpkg.add("brycewang-stanford-election-data-source-countypres")
if result.exit_code:
    raise SystemExit(result.problems)

print("Added. Start Claude Code with the command below.")

Start Claude Code with it

claude --plugin-dir "$(git rev-parse --show-toplevel 2>/dev/null || pwd)/.agents"

Type these in a Claude Code session. No account or API key. It writes the skill and any files it bundles, and asks first when its safety rating isn't Passed.

Add the DecimalAI plugin, once

/plugin marketplace add decimal-labs/decimalai-claude-plugins
/plugin install decimalai@decimalai

Install this skill

/decimalai:install brycewang-stanford-election-data-source-countypres

The plugin needs python3 and curl on your machine.

No Python or account. Claude Code picks it up in its next session.

Save it into your project

curl -fsSL --create-dirs -o .claude/skills/brycewang-stanford-election-data-source-countypres/SKILL.md https://app.decimal.ai/s/brycewang-stanford-election-data-source-countypres/SKILL.md

Copy SKILL.md

Save it in your project, as

.claude/skills/brycewang-stanford-election-data-source-countypres/SKILL.md

This gets SKILL.md only. The skill's 11 other files are not included.

Other ways to add it

Claude Code docs

agent_config() hands your agent the skill. With no DecimalAI key it reads your project's files and sends nothing. Needs SDK 0.27 or newer.

Install

pip install "decimalai[claude-agent-sdk]"
decimalai skills add brycewang-stanford-election-data-source-countypres

Add it to your agent

import asyncio

from claude_agent_sdk import ClaudeAgentOptions
from decimalai.claude_agent_sdk import agent_config

# With no DECIMAL_API_KEY this reads the skills your project lists, from disk.
support = agent_config("support", fallback="You are a helpful agent.")

async def main():
    question = "Hello!"
    async with support.run(question) as run:  # one user message, one run
        async for message in run.query(options=ClaudeAgentOptions(max_turns=6)):
            print(message)

# In a notebook or async code: await main()
asyncio.run(main())

Prefer its own loader? ClaudeAgentOptions(plugins=[skills_plugin()], skills="all") reads the same folder. Use one or the other: a skill delivered both ways reaches the prompt twice.

The same install from Python, for a notebook or a setup script. agent_config() hands your agent the skill. With no DecimalAI key it reads your project's files and sends nothing. Needs SDK 0.27 or newer.

Install

pip install "decimalai[claude-agent-sdk]"

Add it to your agent

from decimalai import skillpkg

# Writes .agents/skills and .decimal/skills.toml. Safe to run twice.
result = skillpkg.add("brycewang-stanford-election-data-source-countypres")
if result.exit_code:
    raise SystemExit(result.problems)

import asyncio

from claude_agent_sdk import ClaudeAgentOptions
from decimalai.claude_agent_sdk import agent_config

# With no DECIMAL_API_KEY this reads the skills your project lists, from disk.
support = agent_config("support", fallback="You are a helpful agent.")

async def main():
    question = "Hello!"
    async with support.run(question) as run:  # one user message, one run
        async for message in run.query(options=ClaudeAgentOptions(max_turns=6)):
            print(message)

# In a notebook or async code: await main()
asyncio.run(main())

Prefer its own loader? ClaudeAgentOptions(plugins=[skills_plugin()], skills="all") reads the same folder. Use one or the other: a skill delivered both ways reaches the prompt twice.

No DecimalAI package. The whole skill goes in every prompt, and nothing pins or updates it.

Copy SKILL.md

Save it in your project, as

.agents/skills/brycewang-stanford-election-data-source-countypres/SKILL.md

Give it to your agent

import asyncio
from pathlib import Path
from claude_agent_sdk import ClaudeAgentOptions, query

skill = Path(".agents/skills/brycewang-stanford-election-data-source-countypres/SKILL.md").read_text()
options = ClaudeAgentOptions(system_prompt=f"You are a helpful agent.\n\n{skill}", max_turns=6)

async def main():
    async for message in query(prompt="Hello!", options=options):
        print(message)

# In a notebook or async code: await main()
asyncio.run(main())

This gets SKILL.md only. The skill's 11 other files are not included.

Other ways to add it

Claude Agent SDK docs

agent_config() hands your agent the skill. With no DecimalAI key it reads your project's files and sends nothing. Needs SDK 0.27 or newer.

Install

pip install "decimalai[openai-agents]"
decimalai skills add brycewang-stanford-election-data-source-countypres

Add it to your agent

from agents import Agent, Runner
from decimalai.openai_agents import agent_config

# With no DECIMAL_API_KEY this reads the skills your project lists, from disk.
support = agent_config("support", fallback="You are a helpful agent.")

agent = Agent(
    name=support.name,
    instructions=support.instructions,  # your prompt, then the skill list
    tools=[*support.tools],             # your tools, then load_skill
)
# In a notebook or async code: result = await Runner.run(agent, "Hello!")
result = Runner.run_sync(agent, "Hello!")

Using SandboxAgent? capabilities=[Shell(), decimalai.openai_agents.sandbox_skills()] points its own loader at the same folder.

Install

pip install "decimalai[openai-agents]"

Add it to your agent

from decimalai import skillpkg

# Writes .agents/skills and .decimal/skills.toml. Safe to run twice.
result = skillpkg.add("brycewang-stanford-election-data-source-countypres")
if result.exit_code:
    raise SystemExit(result.problems)

from agents import Agent, Runner
from decimalai.openai_agents import agent_config

# With no DECIMAL_API_KEY this reads the skills your project lists, from disk.
support = agent_config("support", fallback="You are a helpful agent.")

agent = Agent(
    name=support.name,
    instructions=support.instructions,  # your prompt, then the skill list
    tools=[*support.tools],             # your tools, then load_skill
)
# In a notebook or async code: result = await Runner.run(agent, "Hello!")
result = Runner.run_sync(agent, "Hello!")

Using SandboxAgent? capabilities=[Shell(), decimalai.openai_agents.sandbox_skills()] points its own loader at the same folder.

No DecimalAI package. The whole skill goes in every prompt, and nothing pins or updates it.

Copy SKILL.md

Save it in your project, as

.agents/skills/brycewang-stanford-election-data-source-countypres/SKILL.md

Give it to your agent

from pathlib import Path
from agents import Agent, Runner

skill = Path(".agents/skills/brycewang-stanford-election-data-source-countypres/SKILL.md").read_text()
agent = Agent(name="support", instructions=f"You are a helpful agent.\n\n{skill}")
# In a notebook or async code: result = await Runner.run(agent, "Hello!")
result = Runner.run_sync(agent, "Hello!")

This gets SKILL.md only. The skill's 11 other files are not included.

Other ways to add it

OpenAI Agents docs

agent_config() hands your agent the skill. With no DecimalAI key it reads your project's files and sends nothing. Needs SDK 0.27 or newer.

Install

pip install "decimalai[openai]"
decimalai skills add brycewang-stanford-election-data-source-countypres

Add it to your agent

import json

from openai import OpenAI
from decimalai.openai import agent_config

client = OpenAI()
# With no DECIMAL_API_KEY this reads the skills your project lists, from disk.
support = agent_config("support", fallback="You are a helpful agent.")


def lookup_order(order_id: str) -> str:
    return f"Order {order_id} shipped yesterday."


# Your tools, as Chat Completions takes them, and what answers each.
TOOLS = [{"type": "function", "function": {
    "name": "lookup_order",
    "description": "Look up the status of an order.",
    "parameters": {"type": "object", "properties": {"order_id": {"type": "string"}},
                   "required": ["order_id"]},
}}]
FUNCTIONS = {"lookup_order": lookup_order}

question = "Where is order A1001?"
with support.run(question) as run:  # one user message, one run
    # run.system is your prompt, then the skill list.
    messages = [{"role": "system", "content": run.system}, run.message]
    while True:
        reply = client.chat.completions.create(
            model="gpt-5.4-mini",
            messages=messages,
            tools=[*TOOLS, *run.tools],  # your tools, then load_skill
        ).choices[0].message
        messages.append(reply)
        if not reply.tool_calls:
            break
        for call in reply.tool_calls:
            # load_skill is answered by the run; your own tools by FUNCTIONS.
            function = FUNCTIONS.get(call.function.name)
            messages.append(run.tool_result(call) or {
                "role": "tool", "tool_call_id": call.id,
                "content": function(**json.loads(call.function.arguments)) if function
                else f"There is no tool named {call.function.name!r}.",
            })
print(reply.content)

# The Responses API takes run.response_tools instead of run.tools.

Install

pip install "decimalai[openai]"

Add it to your agent

from decimalai import skillpkg

# Writes .agents/skills and .decimal/skills.toml. Safe to run twice.
result = skillpkg.add("brycewang-stanford-election-data-source-countypres")
if result.exit_code:
    raise SystemExit(result.problems)

import json

from openai import OpenAI
from decimalai.openai import agent_config

client = OpenAI()
# With no DECIMAL_API_KEY this reads the skills your project lists, from disk.
support = agent_config("support", fallback="You are a helpful agent.")


def lookup_order(order_id: str) -> str:
    return f"Order {order_id} shipped yesterday."


# Your tools, as Chat Completions takes them, and what answers each.
TOOLS = [{"type": "function", "function": {
    "name": "lookup_order",
    "description": "Look up the status of an order.",
    "parameters": {"type": "object", "properties": {"order_id": {"type": "string"}},
                   "required": ["order_id"]},
}}]
FUNCTIONS = {"lookup_order": lookup_order}

question = "Where is order A1001?"
with support.run(question) as run:  # one user message, one run
    # run.system is your prompt, then the skill list.
    messages = [{"role": "system", "content": run.system}, run.message]
    while True:
        reply = client.chat.completions.create(
            model="gpt-5.4-mini",
            messages=messages,
            tools=[*TOOLS, *run.tools],  # your tools, then load_skill
        ).choices[0].message
        messages.append(reply)
        if not reply.tool_calls:
            break
        for call in reply.tool_calls:
            # load_skill is answered by the run; your own tools by FUNCTIONS.
            function = FUNCTIONS.get(call.function.name)
            messages.append(run.tool_result(call) or {
                "role": "tool", "tool_call_id": call.id,
                "content": function(**json.loads(call.function.arguments)) if function
                else f"There is no tool named {call.function.name!r}.",
            })
print(reply.content)

# The Responses API takes run.response_tools instead of run.tools.

No DecimalAI package. The whole skill goes in every prompt, and nothing pins or updates it.

Copy SKILL.md

Save it in your project, as

.agents/skills/brycewang-stanford-election-data-source-countypres/SKILL.md

Give it to your agent

from pathlib import Path
from openai import OpenAI

client = OpenAI()
skill = Path(".agents/skills/brycewang-stanford-election-data-source-countypres/SKILL.md").read_text()
reply = client.chat.completions.create(
    model="gpt-5.4-mini",
    messages=[
        {"role": "system", "content": f"You are a helpful agent.\n\n{skill}"},
        {"role": "user", "content": "Hello!"},
    ],
).choices[0].message

This gets SKILL.md only. The skill's 11 other files are not included.

Other ways to add it

OpenAI SDK docs

agent_config() hands your agent the skill. With no DecimalAI key it reads your project's files and sends nothing. Needs SDK 0.27 or newer.

Install

pip install "decimalai[anthropic]"
decimalai skills add brycewang-stanford-election-data-source-countypres

Add it to your agent

import anthropic
from decimalai.anthropic import agent_config

client = anthropic.Anthropic()
# With no DECIMAL_API_KEY this reads the skills your project lists, from disk.
support = agent_config("support", fallback="You are a helpful agent.")

question = "Hello!"
with support.run(question) as run:  # one user message, one run
    answer = client.beta.messages.tool_runner(
        model="claude-haiku-5-5",
        max_tokens=4096,
        system=run.system,     # your prompt, then the skill list
        tools=[*run.tools],    # your tools, then load_skill
        messages=[{"role": "user", "content": question}],
    ).until_done()

Install

pip install "decimalai[anthropic]"

Add it to your agent

from decimalai import skillpkg

# Writes .agents/skills and .decimal/skills.toml. Safe to run twice.
result = skillpkg.add("brycewang-stanford-election-data-source-countypres")
if result.exit_code:
    raise SystemExit(result.problems)

import anthropic
from decimalai.anthropic import agent_config

client = anthropic.Anthropic()
# With no DECIMAL_API_KEY this reads the skills your project lists, from disk.
support = agent_config("support", fallback="You are a helpful agent.")

question = "Hello!"
with support.run(question) as run:  # one user message, one run
    answer = client.beta.messages.tool_runner(
        model="claude-haiku-5-5",
        max_tokens=4096,
        system=run.system,     # your prompt, then the skill list
        tools=[*run.tools],    # your tools, then load_skill
        messages=[{"role": "user", "content": question}],
    ).until_done()

No DecimalAI package. The whole skill goes in every prompt, and nothing pins or updates it.

Copy SKILL.md

Save it in your project, as

.agents/skills/brycewang-stanford-election-data-source-countypres/SKILL.md

Give it to your agent

from pathlib import Path
import anthropic

client = anthropic.Anthropic()
skill = Path(".agents/skills/brycewang-stanford-election-data-source-countypres/SKILL.md").read_text()
reply = client.messages.create(
    model="claude-haiku-5-5",
    max_tokens=4096,
    system=f"You are a helpful agent.\n\n{skill}",
    messages=[{"role": "user", "content": "Hello!"}],
)

This gets SKILL.md only. The skill's 11 other files are not included.

Other ways to add it

Anthropic docs

agent_config() hands your agent the skill. With no DecimalAI key it reads your project's files and sends nothing. Needs SDK 0.27 or newer.

Install

pip install "decimalai[google-genai]"
decimalai skills add brycewang-stanford-election-data-source-countypres

Add it to your agent

from google import genai
from google.genai import types
from decimalai.google_genai import agent_config

client = genai.Client()
# With no DECIMAL_API_KEY this reads the skills your project lists, from disk.
support = agent_config("support", fallback="You are a helpful agent.")


def lookup_order(order_id: str) -> str:
    return f"Order {order_id} shipped yesterday."


# Your functions, as declarations for the model, and what answers each.
TOOLS = [{"function_declarations": [{
    "name": "lookup_order",
    "description": "Look up the status of an order.",
    "parameters_json_schema": {"type": "object", "properties": {"order_id": {"type": "string"}},
                               "required": ["order_id"]},
}]}]
FUNCTIONS = {"lookup_order": lookup_order}

question = "Where is order A1001?"
with support.run(question) as run:  # one user message, one run
    config = types.GenerateContentConfig(
        system_instruction=run.system,     # your prompt, then the skill list
        tools=[*TOOLS, *run.tool_params],  # your functions, then load_skill
    )
    contents = [{"role": "user", "parts": [{"text": run.message}]}]
    while True:
        response = client.models.generate_content(
            model="gemini-3.5-flash", contents=contents, config=config,
        )
        if not response.function_calls:
            break
        contents.append(response.candidates[0].content)
        parts = []
        for call in response.function_calls:
            # load_skill is answered by the run; your own functions by FUNCTIONS.
            # A loop of your own rather than automatic function calling, which
            # raises KeyError when the model asks for a function you did not pass.
            function = FUNCTIONS.get(call.name)
            parts.append(run.tool_result(call) or {"function_response": {
                "name": call.name, "id": call.id,
                "response": {"result": function(**(call.args or {})) if function
                             else f"There is no function named {call.name!r}."},
            }})
        contents.append({"role": "user", "parts": parts})
print(response.text)

Install

pip install "decimalai[google-genai]"

Add it to your agent

from decimalai import skillpkg

# Writes .agents/skills and .decimal/skills.toml. Safe to run twice.
result = skillpkg.add("brycewang-stanford-election-data-source-countypres")
if result.exit_code:
    raise SystemExit(result.problems)

from google import genai
from google.genai import types
from decimalai.google_genai import agent_config

client = genai.Client()
# With no DECIMAL_API_KEY this reads the skills your project lists, from disk.
support = agent_config("support", fallback="You are a helpful agent.")


def lookup_order(order_id: str) -> str:
    return f"Order {order_id} shipped yesterday."


# Your functions, as declarations for the model, and what answers each.
TOOLS = [{"function_declarations": [{
    "name": "lookup_order",
    "description": "Look up the status of an order.",
    "parameters_json_schema": {"type": "object", "properties": {"order_id": {"type": "string"}},
                               "required": ["order_id"]},
}]}]
FUNCTIONS = {"lookup_order": lookup_order}

question = "Where is order A1001?"
with support.run(question) as run:  # one user message, one run
    config = types.GenerateContentConfig(
        system_instruction=run.system,     # your prompt, then the skill list
        tools=[*TOOLS, *run.tool_params],  # your functions, then load_skill
    )
    contents = [{"role": "user", "parts": [{"text": run.message}]}]
    while True:
        response = client.models.generate_content(
            model="gemini-3.5-flash", contents=contents, config=config,
        )
        if not response.function_calls:
            break
        contents.append(response.candidates[0].content)
        parts = []
        for call in response.function_calls:
            # load_skill is answered by the run; your own functions by FUNCTIONS.
            # A loop of your own rather than automatic function calling, which
            # raises KeyError when the model asks for a function you did not pass.
            function = FUNCTIONS.get(call.name)
            parts.append(run.tool_result(call) or {"function_response": {
                "name": call.name, "id": call.id,
                "response": {"result": function(**(call.args or {})) if function
                             else f"There is no function named {call.name!r}."},
            }})
        contents.append({"role": "user", "parts": parts})
print(response.text)

No DecimalAI package. The whole skill goes in every prompt, and nothing pins or updates it.

Copy SKILL.md

Save it in your project, as

.agents/skills/brycewang-stanford-election-data-source-countypres/SKILL.md

Give it to your agent

from pathlib import Path
from google import genai
from google.genai import types

client = genai.Client()
skill = Path(".agents/skills/brycewang-stanford-election-data-source-countypres/SKILL.md").read_text()
response = client.models.generate_content(
    model="gemini-3.5-flash",
    contents="Hello!",
    config=types.GenerateContentConfig(system_instruction=f"You are a helpful agent.\n\n{skill}"),
)

This gets SKILL.md only. The skill's 11 other files are not included.

Other ways to add it

Gemini API docs

agent_config() hands your agent the skill. With no DecimalAI key it reads your project's files and sends nothing. Needs SDK 0.27 or newer.

Install

pip install "decimalai[langchain]" langchain-openai
decimalai skills add brycewang-stanford-election-data-source-countypres

Add it to your agent

from langchain.agents import create_agent
from decimalai.langchain import agent_config

# With no DECIMAL_API_KEY this reads the skills your project lists, from disk.
support = agent_config("support", fallback="You are a helpful agent.")

agent = create_agent(
    "openai:gpt-5.4-mini",
    tools=[],                         # your tools; the middleware adds load_skill
    middleware=[support.middleware],  # your prompt, the skill list and load_skill
)
result = agent.invoke({"messages": [{"role": "user", "content": "Hello!"}]})

Install

pip install "decimalai[langchain]" langchain-openai

Add it to your agent

from decimalai import skillpkg

# Writes .agents/skills and .decimal/skills.toml. Safe to run twice.
result = skillpkg.add("brycewang-stanford-election-data-source-countypres")
if result.exit_code:
    raise SystemExit(result.problems)

from langchain.agents import create_agent
from decimalai.langchain import agent_config

# With no DECIMAL_API_KEY this reads the skills your project lists, from disk.
support = agent_config("support", fallback="You are a helpful agent.")

agent = create_agent(
    "openai:gpt-5.4-mini",
    tools=[],                         # your tools; the middleware adds load_skill
    middleware=[support.middleware],  # your prompt, the skill list and load_skill
)
result = agent.invoke({"messages": [{"role": "user", "content": "Hello!"}]})

No DecimalAI package. The whole skill goes in every prompt, and nothing pins or updates it.

Copy SKILL.md

Save it in your project, as

.agents/skills/brycewang-stanford-election-data-source-countypres/SKILL.md

Give it to your agent

from pathlib import Path
from langchain.agents import create_agent

skill = Path(".agents/skills/brycewang-stanford-election-data-source-countypres/SKILL.md").read_text()
agent = create_agent("openai:gpt-5.4-mini", tools=[], system_prompt=f"You are a helpful agent.\n\n{skill}")
result = agent.invoke({"messages": [{"role": "user", "content": "Hello!"}]})

This gets SKILL.md only. The skill's 11 other files are not included.

Other ways to add it

LangChain docs

CrewAI's own skill loader reads the installed folder. No DecimalAI account needed.

Install

pip install "decimalai>=0.16" "crewai>=1.15.27"
decimalai skills add brycewang-stanford-election-data-source-countypres

Add it to your agent

import decimalai.crewai
from crewai import Agent, Crew, Task

agent = Agent(
    role="Support", goal="Help the customer", backstory="A support agent.",
    llm=llm,                               # your own CrewAI LLM
    skills=decimalai.crewai.skills(),      # the installed folder
    tools=decimalai.crewai.skill_tools(),  # reads a skill's files, runs its scripts
)
task = Task(description="Hello!", expected_output="an answer", agent=agent)
Crew(agents=[agent], tasks=[task]).kickoff()

The same install from Python, for a notebook or a setup script. CrewAI's own skill loader reads the installed folder. No DecimalAI account needed.

Install

pip install "decimalai>=0.16" "crewai>=1.15.27"

Add it to your agent

from decimalai import skillpkg

# Writes .agents/skills and .decimal/skills.toml. Safe to run twice.
result = skillpkg.add("brycewang-stanford-election-data-source-countypres")
if result.exit_code:
    raise SystemExit(result.problems)

import decimalai.crewai
from crewai import Agent, Crew, Task

agent = Agent(
    role="Support", goal="Help the customer", backstory="A support agent.",
    llm=llm,                               # your own CrewAI LLM
    skills=decimalai.crewai.skills(),      # the installed folder
    tools=decimalai.crewai.skill_tools(),  # reads a skill's files, runs its scripts
)
task = Task(description="Hello!", expected_output="an answer", agent=agent)
Crew(agents=[agent], tasks=[task]).kickoff()

No DecimalAI package. CrewAI's own loader reads the folder, and nothing pins or updates it.

Copy SKILL.md

Save it in your project, as

.agents/skills/brycewang-stanford-election-data-source-countypres/SKILL.md

Give it to your agent

from pathlib import Path
from crewai import Agent, Crew, Task

agent = Agent(
    role="Support", goal="Help the customer", backstory="A support agent.",
    llm=llm,                         # your own CrewAI LLM
    skills=[Path(".agents/skills")],
)
task = Task(description="Hello!", expected_output="an answer", agent=agent)
Crew(agents=[agent], tasks=[task]).kickoff()

This gets SKILL.md only. The skill's 11 other files are not included.

Other ways to add it

CrewAI docs

agent_config() hands your agent the skill. With no DecimalAI key it reads your project's files and sends nothing. Needs SDK 0.27 or newer.

Install

pip install "decimalai[adk]"
decimalai skills add brycewang-stanford-election-data-source-countypres

Add it to your agent

from decimalai.adk import DecimalAIPlugin, agent_config
from google.adk.agents import LlmAgent
from google.adk.apps import App

# With no DECIMAL_API_KEY this reads the skills your project lists, from disk.
support = agent_config("support", fallback="You are a helpful agent.")

agent = LlmAgent(
    name="support",          # ADK needs a Python identifier
    model="gemini-3.5-flash",
    instruction=support.instruction,  # your prompt, then the skill list
    tools=[*support.tools],           # your tools, then load_skill
)
# DecimalAIPlugin makes each invocation of runners built from this App one trace.
app = App(name="support", root_agent=agent, plugins=[DecimalAIPlugin()])

Prefer ADK's own loader? SkillToolset(skills=decimalai.adk.skills(), ...) reads the same folder. Use one or the other: a skill delivered both ways reaches the prompt twice.

Install

pip install "decimalai[adk]"

Add it to your agent

from decimalai import skillpkg

# Writes .agents/skills and .decimal/skills.toml. Safe to run twice.
result = skillpkg.add("brycewang-stanford-election-data-source-countypres")
if result.exit_code:
    raise SystemExit(result.problems)

from decimalai.adk import DecimalAIPlugin, agent_config
from google.adk.agents import LlmAgent
from google.adk.apps import App

# With no DECIMAL_API_KEY this reads the skills your project lists, from disk.
support = agent_config("support", fallback="You are a helpful agent.")

agent = LlmAgent(
    name="support",          # ADK needs a Python identifier
    model="gemini-3.5-flash",
    instruction=support.instruction,  # your prompt, then the skill list
    tools=[*support.tools],           # your tools, then load_skill
)
# DecimalAIPlugin makes each invocation of runners built from this App one trace.
app = App(name="support", root_agent=agent, plugins=[DecimalAIPlugin()])

Prefer ADK's own loader? SkillToolset(skills=decimalai.adk.skills(), ...) reads the same folder. Use one or the other: a skill delivered both ways reaches the prompt twice.

No DecimalAI package. The whole skill goes in every prompt, and nothing pins or updates it.

Copy SKILL.md

Save it in your project, as

.agents/skills/brycewang-stanford-election-data-source-countypres/SKILL.md

Give it to your agent

from pathlib import Path
from google.adk.agents import LlmAgent

skill = Path(".agents/skills/brycewang-stanford-election-data-source-countypres/SKILL.md").read_text()
agent = LlmAgent(
    name="support",
    model="gemini-3.5-flash",
    instruction=lambda context: f"You are a helpful agent.\n\n{skill}",
)

This gets SKILL.md only. The skill's 11 other files are not included.

Other ways to add it

Google ADK docs

agent_config() hands your agent the skill. With no DecimalAI key it reads your project's files and sends nothing. Needs SDK 0.27 or newer.

Install

pip install "decimalai[pydantic-ai]"
decimalai skills add brycewang-stanford-election-data-source-countypres

Add it to your agent

from pydantic_ai import Agent
from decimalai.pydantic_ai import agent_config

# With no DECIMAL_API_KEY this reads the skills your project lists, from disk.
support = agent_config("support", fallback="You are a helpful agent.")

agent = Agent(
    "openai:gpt-4o-mini",
    name=support.name,
    tools=[],                 # your tools; the capability adds load_skill
    capabilities=[support],   # your prompt, the skill list and load_skill
)
# In a notebook or async code: result = await agent.run("Hello!")
result = agent.run_sync("Hello!")

On the Pydantic AI harness, decimalai.pydantic_ai_harness.skills(project) uses its own loader instead.

Install

pip install "decimalai[pydantic-ai]"

Add it to your agent

from decimalai import skillpkg

# Writes .agents/skills and .decimal/skills.toml. Safe to run twice.
result = skillpkg.add("brycewang-stanford-election-data-source-countypres")
if result.exit_code:
    raise SystemExit(result.problems)

from pydantic_ai import Agent
from decimalai.pydantic_ai import agent_config

# With no DECIMAL_API_KEY this reads the skills your project lists, from disk.
support = agent_config("support", fallback="You are a helpful agent.")

agent = Agent(
    "openai:gpt-4o-mini",
    name=support.name,
    tools=[],                 # your tools; the capability adds load_skill
    capabilities=[support],   # your prompt, the skill list and load_skill
)
# In a notebook or async code: result = await agent.run("Hello!")
result = agent.run_sync("Hello!")

On the Pydantic AI harness, decimalai.pydantic_ai_harness.skills(project) uses its own loader instead.

No DecimalAI package. The whole skill goes in every prompt, and nothing pins or updates it.

Copy SKILL.md

Save it in your project, as

.agents/skills/brycewang-stanford-election-data-source-countypres/SKILL.md

Give it to your agent

from pathlib import Path
from pydantic_ai import Agent

skill = Path(".agents/skills/brycewang-stanford-election-data-source-countypres/SKILL.md").read_text()
agent = Agent("openai:gpt-4o-mini", instructions=f"You are a helpful agent.\n\n{skill}")
# In a notebook or async code: result = await agent.run("Hello!")
result = agent.run_sync("Hello!")

This gets SKILL.md only. The skill's 11 other files are not included.

Other ways to add it

Pydantic AI docs

Deep Agents' own skill loader reads the installed folder. No DecimalAI account needed.

Install

pip install "decimalai>=0.16" deepagents
decimalai skills add brycewang-stanford-election-data-source-countypres

Add it to your agent

import decimalai.deepagents
from deepagents import create_deep_agent

agent = create_deep_agent(model=model, **decimalai.deepagents.skills())
agent.invoke({"messages": [{"role": "user", "content": "Hello!"}]})

The default backend reads files but has no shell. To run a skill's scripts, pass skills(backend=LocalShellBackend(...)).

The same install from Python, for a notebook or a setup script. Deep Agents' own skill loader reads the installed folder. No DecimalAI account needed.

Install

pip install "decimalai>=0.16" deepagents

Add it to your agent

from decimalai import skillpkg

# Writes .agents/skills and .decimal/skills.toml. Safe to run twice.
result = skillpkg.add("brycewang-stanford-election-data-source-countypres")
if result.exit_code:
    raise SystemExit(result.problems)

import decimalai.deepagents
from deepagents import create_deep_agent

agent = create_deep_agent(model=model, **decimalai.deepagents.skills())
agent.invoke({"messages": [{"role": "user", "content": "Hello!"}]})

The default backend reads files but has no shell. To run a skill's scripts, pass skills(backend=LocalShellBackend(...)).

No DecimalAI package. The whole skill goes in every prompt, and nothing pins or updates it.

Copy SKILL.md

Save it in your project, as

.agents/skills/brycewang-stanford-election-data-source-countypres/SKILL.md

Give it to your agent

from pathlib import Path
from deepagents import create_deep_agent

skill = Path(".agents/skills/brycewang-stanford-election-data-source-countypres/SKILL.md").read_text()
agent = create_deep_agent(model=model, system_prompt=f"You are a helpful agent.\n\n{skill}")
agent.invoke({"messages": [{"role": "user", "content": "Hello!"}]})

This gets SKILL.md only. The skill's 11 other files are not included.

Other ways to add it

Deep Agents docs

Its own skill loader reads the installed folder. No DecimalAI account needed.

Install

pip install "decimalai>=0.16" agent-framework
decimalai skills add brycewang-stanford-election-data-source-countypres

Add it to your agent

import asyncio

from agent_framework import Agent
from decimalai.agent_framework import skills

agent = Agent(client=client, instructions="You are a helpful agent.", context_providers=[skills()])
asyncio.run(agent.run("Hello!"))

It caches skills by default, so restart the process after decimalai skills update.

The same install from Python, for a notebook or a setup script. Its own skill loader reads the installed folder. No DecimalAI account needed.

Install

pip install "decimalai>=0.16" agent-framework

Add it to your agent

from decimalai import skillpkg

# Writes .agents/skills and .decimal/skills.toml. Safe to run twice.
result = skillpkg.add("brycewang-stanford-election-data-source-countypres")
if result.exit_code:
    raise SystemExit(result.problems)

import asyncio

from agent_framework import Agent
from decimalai.agent_framework import skills

agent = Agent(client=client, instructions="You are a helpful agent.", context_providers=[skills()])
asyncio.run(agent.run("Hello!"))

It caches skills by default, so restart the process after decimalai skills update.

No DecimalAI package. The whole skill goes in every prompt, and nothing pins or updates it.

Copy SKILL.md

Save it in your project, as

.agents/skills/brycewang-stanford-election-data-source-countypres/SKILL.md

Give it to your agent

import asyncio
from pathlib import Path
from agent_framework import Agent

skill = Path(".agents/skills/brycewang-stanford-election-data-source-countypres/SKILL.md").read_text()
agent = Agent(client=client, instructions=f"You are a helpful agent.\n\n{skill}")
asyncio.run(agent.run("Hello!"))

This gets SKILL.md only. The skill's 11 other files are not included.

Other ways to add it

Microsoft Agent Framework docs

Strands' own skill loader reads the installed folder. No DecimalAI account needed.

Install

pip install "decimalai>=0.16" strands-agents
decimalai skills add brycewang-stanford-election-data-source-countypres

Add it to your agent

from decimalai.strands import skills
from strands import Agent
from strands.vended_tools import file_editor, shell

agent = Agent(
    model=model,                # always pass one: the default is Amazon Bedrock
    system_prompt="You are a helpful agent.",
    tools=[file_editor, shell],
    plugins=[skills()],
)
agent("Hello!")

Strands loads an agent's skills once, so build the agent again after decimalai skills update.

The same install from Python, for a notebook or a setup script. Strands' own skill loader reads the installed folder. No DecimalAI account needed.

Install

pip install "decimalai>=0.16" strands-agents

Add it to your agent

from decimalai import skillpkg

# Writes .agents/skills and .decimal/skills.toml. Safe to run twice.
result = skillpkg.add("brycewang-stanford-election-data-source-countypres")
if result.exit_code:
    raise SystemExit(result.problems)

from decimalai.strands import skills
from strands import Agent
from strands.vended_tools import file_editor, shell

agent = Agent(
    model=model,                # always pass one: the default is Amazon Bedrock
    system_prompt="You are a helpful agent.",
    tools=[file_editor, shell],
    plugins=[skills()],
)
agent("Hello!")

Strands loads an agent's skills once, so build the agent again after decimalai skills update.

No DecimalAI package. The whole skill goes in every prompt, and nothing pins or updates it.

Copy SKILL.md

Save it in your project, as

.agents/skills/brycewang-stanford-election-data-source-countypres/SKILL.md

Give it to your agent

from pathlib import Path
from strands import Agent

skill = Path(".agents/skills/brycewang-stanford-election-data-source-countypres/SKILL.md").read_text()
agent = Agent(model=model, system_prompt=f"You are a helpful agent.\n\n{skill}")
agent("Hello!")

This gets SKILL.md only. The skill's 11 other files are not included.

Other ways to add it

Strands docs

Adds every file the skill has, pinned so you can update it. Cursor, Copilot, Cline and Warp read this folder by themselves.

pip install "decimalai>=0.15"
decimalai skills add brycewang-stanford-election-data-source-countypres

No Python or account. Cursor, Copilot, Cline and Warp read this folder by themselves.

Save it into your project

curl -fsSL --create-dirs -o .agents/skills/brycewang-stanford-election-data-source-countypres/SKILL.md https://app.decimal.ai/s/brycewang-stanford-election-data-source-countypres/SKILL.md

Copy SKILL.md

Save it in your project, as

.agents/skills/brycewang-stanford-election-data-source-countypres/SKILL.md

This gets SKILL.md only. The skill's 11 other files are not included.

Other ways to add it

Cursor and other editors docs

Fetch the file and give its text to your model as instructions. No account or package needed.

Get the file

curl -fsSL https://app.decimal.ai/s/brycewang-stanford-election-data-source-countypres/SKILL.md

Read the summary as JSON

curl -fsSL https://app.decimal.ai/s/brycewang-stanford-election-data-source-countypres.json

This gets SKILL.md only. The skill's 11 other files are not included.

Other ways to add it

Other setups docs

You don't need a DecimalAI account.

Version: v1, tested 8/9/2026
Source: brycewang-stanford/Auto-Empirical-Research-Skills ↗
License: NOASSERTION

Manage it in DecimalAI

Saved prompts and skills, pinned versions, and traces of this skill in your runs. DecimalAI does not run your agent.

Claude Code reads files from your project, so DecimalAI config does not apply there.

On Claude Agent SDK: save the skill to an agent here, set DECIMAL_API_KEY, and the same code uses it with no command to run. Changes you save reach the next run with no redeploy.

On OpenAI Agents: save the skill to an agent here, set DECIMAL_API_KEY, and the same code uses it with no command to run. Changes you save reach the next run with no redeploy.

On OpenAI SDK: save the skill to an agent here, set DECIMAL_API_KEY, and the same code uses it with no command to run. Changes you save reach the next run with no redeploy.

On Anthropic: save the skill to an agent here, set DECIMAL_API_KEY, and the same code uses it with no command to run. Changes you save reach the next run with no redeploy.

On Gemini API: save the skill to an agent here, set DECIMAL_API_KEY, and the same code uses it with no command to run. Changes you save reach the next run with no redeploy.

On LangChain: save the skill to an agent here, set DECIMAL_API_KEY, and the same code uses it with no command to run. Changes you save reach the next run with no redeploy.

On CrewAI: set DECIMAL_API_KEY and add decimalai.init(crewai=True) to record runs and skill use. The skill version stays in your repo.

On Google ADK: save the skill to an agent here, set DECIMAL_API_KEY, and the same code uses it with no command to run. Changes you save reach the next run with no redeploy.

On Pydantic AI: save the skill to an agent here, set DECIMAL_API_KEY, and the same code uses it with no command to run. Changes you save reach the next run with no redeploy.

On Deep Agents: set DECIMAL_API_KEY and add decimalai.init(langchain=True) to record runs and skill use. The skill version stays in your repo.

On Microsoft Agent Framework: set DECIMAL_API_KEY and add decimalai.init(otel=True, agent_name="support") to record runs and skill use. The skill version stays in your repo.

On Strands: set DECIMAL_API_KEY and add decimalai.init(otel=True, agent_name="support") to record runs and skill use. The skill version stays in your repo.

Editors read files from your project, so DecimalAI config does not apply there.

Anywhere else: record a use with decimalai.log_skill_activation() inside a trace.

Use this skill

SKILL.md

County Presidential Data Source Reference

County Presidential Election Returns 2000-2024 from MIT Election Data and Science Lab (MEDSL). Use when analyzing county-level presidential vote shares, party trends, turnout, or geographic voting patterns. Key join column county_fips enables linking to census, education (CCD/SAIPE), and demographic datasets. Requires Harvard Dataverse API key (HARVARD_DATAVERSE_API_KEY env var). Categorical variables use uppercase strings, not Portal integer codes. Critical caveat: naive mode='TOTAL' filtering silently drops ~1,000 counties in 2020+ data — use 3-pattern reconstruction.

The authoritative source for county-level U.S. presidential election returns spanning 2000-2024. Provides candidate-level vote counts across all 50 states and DC, enabling vote share analysis, partisan trend mapping, and cross-domain geographic research via FIPS code joins.

CRITICAL: Value Encoding

This dataset uses uppercase string codes for categorical variables (party, mode, candidate, state) rather than integer codes. Empty strings ("") appear as undocumented values in party (501 rows, 2024) and mode (2,795 rows, 2024).

Context party mode candidate
Standard values DEMOCRAT, REPUBLICAN TOTAL BARACK OBAMA
Aggregate/meta values OTHER, "" "", ELECTION DAY OTHER, UNDERVOTES

See ./references/variable-definitions.md for complete encoding tables.

Context	party	mode	candidate
Standard values	`DEMOCRAT`, `REPUBLICAN`	`TOTAL`	`BARACK OBAMA`
Aggregate/meta values	`OTHER`, `""`	`""`, `ELECTION DAY`	`OTHER`, `UNDERVOTES`

Prerequisites

API Key Required: This data source requires a Harvard Dataverse API key to fetch data. Unlike education data sources (which use the Urban Institute's free, unauthenticated API), election data is hosted on Harvard Dataverse and requires authentication.

Setup instructions:
Create a free Harvard Dataverse account at https://dataverse.harvard.edu/

Log in, navigate to your account name (top-right) → API Token

Click "Create Token" and copy it
Set the environment variable before launching Claude Code:
export HARVARD_DATAVERSE_API_KEY="your_token_here"
For Docker users: run this inside the container after docker compose exec daaf-docker bash but before claude. To make it persistent across sessions, add it to ~/.bashrc.
If the key is missing, any fetch script will fail with a KeyError: 'HARVARD_DATAVERSE_API_KEY'. The orchestrator should check for this variable's existence before dispatching Stage 5 fetch tasks that use this data source.

What is the MEDSL County Presidential Returns Dataset?

Producer: MIT Election Data and Science Lab (MEDSL)
Coverage: County-level presidential election returns, 50 states + DC
Frequency: Every 4 years (presidential election cycle)
Available years: 2000, 2004, 2008, 2012, 2016, 2020, 2024
Primary identifier: county_fips (5-digit FIPS code, stored as integer)
Record unit: One row per county-year-candidate-party-mode combination
Total records: 94,151 rows x 12 columns (~8.4 MB). Note: rows per year vary dramatically — 2020/2024 have ~2x rows due to mode breakdowns (~22K vs ~9.5K for earlier years)
Source: Harvard Dataverse (DOI: 10.7910/DVN/VOQCHQ)

Reference File Structure

File	Purpose	When to Read
`variable-definitions.md`	Complete column specs, party/mode/candidate value tables	Interpreting specific columns or coded values
`coded-values.md`	All categorical value mappings with frequencies	Filtering or recoding party, mode, candidate
`columns.md`	Detailed per-column profiling (types, nulls, ranges)	Understanding column characteristics
`quality-notes.md`	Known issues, anomalies, duplicates, null patterns	Assessing data reliability
`mode-reconstruction.md`	3-pattern TOTAL mode reconstruction for 2020+ data	Cleaning any 2020+ analysis (CRITICAL)
`interpretations.md`	Preliminary semantic interpretations (flagged for review)	Understanding column meanings

Decision Trees

What analysis do I need?

Analyzing presidential election data?
├─ County-level vote shares → Use 3-pattern mode reconstruction (./references/mode-reconstruction.md)
│   └─ Longitudinal (cross-year) → MUST reconstruct TOTAL for 2020+ (naive filter drops ~1,000 counties)
│   └─ Single year (pre-2020) → Safe to filter mode='TOTAL'
│   └─ Single year (2020/2024) → Reconstruct unless analyzing a known TOTAL-only state
├─ Party trends → Group by year + party, use party column (not candidate name)
│   └─ Third parties → See ./references/coded-values.md (GREEN/LIBERTARIAN vary by year)
├─ Turnout analysis → Use totalvotes column (dedup per county-year before summing!)
├─ Joining with other data → Use county_fips as join key (zero-pad to 5 chars first!)
│   └─ Census/ACS data → Join on county_fips (standard 5-digit string)
│   └─ Education data (CCD/SAIPE) → Join on county_fips
│   └─ Null FIPS? → See ./references/quality-notes.md (CT, ME, RI)
└─ Voting method analysis → 2020 and 2024 only, see mode breakdown

Is this a data quality issue?

Unexpected values?
├─ county_fips is null → CT/ME/RI in pre-2020 years (52 rows)
├─ county_fips > 72999 → Kansas City MO (FIPS 2938000, non-standard)
├─ county_fips join failures → Zero-pad to 5 chars! (AR codes = 4 digits as int)
├─ AR FIPS 5135 has two counties → Source data error: St. Francis under Sharp County
│   └─ See ./references/quality-notes.md #arkansas-fips-contamination (BLOCKER)
├─ CT counties missing from shapefile → 2022+ TIGER uses planning regions, not counties
│   └─ See ./references/quality-notes.md #connecticut-fips-geography-mismatch
├─ ~1,000 counties missing after mode filter → Use 3-pattern reconstruction, not naive filter
│   └─ See ./references/mode-reconstruction.md
├─ candidate is not a person → UNDERVOTES/OVERVOTES/SPOILED/TOTAL VOTES CAST
│   └─ Filter these OUT for candidate-level analysis
├─ party is empty string → 501 rows in 2024, undocumented
├─ mode is empty string → 2,795 rows in 2024 (may be totals OR breakdowns per state)
├─ candidatevotes is null → 37 rows (NM 2024, mode breakdown)
├─ sum(candidatevotes) > totalvotes → 49 county-years (minor rounding)
├─ Duplicate rows → 83 exact duplicates exist
└─ Alaska 2004 → District-level data, not county; FIPS = 2001-2099
    └─ See ./references/quality-notes.md #alaska-2004

Quick Reference: Election Variables

Party Values by Year

Year	DEMOCRAT	REPUBLICAN	LIBERTARIAN	GREEN	OTHER	`""`
2000	Y	Y	-	Y	Y	-
2004-2016	Y	Y	-	-	Y	-
2020	Y	Y	Y	Y	Y	-
2024	Y	Y	Y	-	Y	Y

Mode Values by Year

Year	Modes Available
2000-2016	`TOTAL` only
2020	`TOTAL` + 15 breakdown modes (11 states)
2024	`TOTAL` + 9 breakdown modes + `""` (varies by state)

For complete mode values see ./references/coded-values.md.

Key Identifiers

ID	Format	Level	Example	Notes
`county_fips`	Int64 (5-digit)	County	`6037` (LA County, CA)	52 nulls (CT/ME/RI); join key for census/education data
`state_po`	String (2-char)	State	`CA`	USPS abbreviation; 1:1 with `state`
`state`	String	State	`CALIFORNIA`	Full uppercase name

WARNING: FIPS Zero-Padding Required for Joins

county_fips is stored as Int64. When converting to string for joins with Census, SAIPE, CCD, or other datasets, zero-pad to 5 characters or Arkansas and other small-FIPS states will produce 4-digit codes that fail to match.
df = df.with_columns(pl.col("county_fips").cast(pl.Utf8).str.zfill(5).alias("county_fips_str"))

Missing Data Codes

Code	Column(s)	Meaning	Frequency
`null`	`county_fips`	FIPS not assigned	52 rows (CT, ME, RI pre-2020)
`null`	`candidatevotes`	Vote count unavailable	37 rows (NM 2024 mode breakdowns)
`0`	`totalvotes`	No votes recorded	50 rows
`0`	`candidatevotes`	Zero votes for candidate	3,908 rows (4.15%)
`""`	`party`	Party not specified	501 rows (2024 only)
`""`	`mode`	Mode not specified	2,795 rows (2024 only)

Non-Candidate Entries in candidate Column

Value	Rows	Meaning
`OTHER`	27,548	Aggregate of minor candidates
`TOTAL VOTES CAST`	427	County total (redundant with totalvotes)
`UNDERVOTES`	402	Ballots with no presidential selection
`OVERVOTES`	380	Ballots with multiple presidential selections
`SPOILED`	14	Invalidated ballots

Filter these out for candidate-level vote share analysis.

Best Practice: Party-Based Identification

Always use party column for identifying party affiliation, never candidate name. Candidate names are inconsistent across years (e.g., "DONALD TRUMP" in 2016 vs "DONALD J TRUMP" in 2020/2024). The party column (DEMOCRAT, REPUBLICAN) is stable across all years.
# CORRECT — stable across years
dem = df.filter(pl.col("party") == "DEMOCRAT")

# WRONG — misses 2016 or 2020/2024 depending on which name you use
trump = df.filter(pl.col("candidate") == "DONALD TRUMP")

Data Access

Dataset Paths

Topic	Type	Path
County presidential returns	Single file	Harvard Dataverse DOI: `10.7910/DVN/VOQCHQ`
Codebook	Single file	Bundled: `County Presidential Returns 2000-2024.md`
Sources per state	Single file	Bundled: `sources-president.tab`

Codebooks

Dataset	Codebook Path
County presidential returns 2000-2024	`County Presidential Returns 2000-2024.md` (bundled in Dataverse)

Codebook is a Markdown file bundled in the Harvard Dataverse deposit. For human reference. The QA methodology paper is at: https://www.nature.com/articles/s41597-022-01745-0

Truth Hierarchy: When interpreting variable values, apply this priority:

Actual data file (what you observe in the TSV) -- this IS the truth

Live codebook (Markdown file in Dataverse) -- authoritative documentation, may lag

This skill documentation -- convenient summary, may drift from codebook

If this documentation contradicts the codebook, trust the codebook. If the codebook contradicts observed data, trust the data and investigate.

Example Fetch

# Fetch from Harvard Dataverse API
import os, requests, polars as pl, io

api_key = os.environ["HARVARD_DATAVERSE_API_KEY"]
# Get file ID from dataset metadata first, then download
# File: countypres_2000-2024.tab (TSV format)
file_url = "https://dataverse.harvard.edu/api/access/datafile/{file_id}"
r = requests.get(file_url, params={"key": api_key, "format": "original"})
df = pl.read_csv(io.BytesIO(r.content), separator='\t')

# Filter to California, 2020, TOTAL mode only
ca_2020 = df.filter(
    (pl.col("state_po") == "CA") &
    (pl.col("year") == 2020) &
    (pl.col("mode") == "TOTAL")
)

Filtering

# Common filter patterns for county presidential data

# 1. Cross-year analysis: WARNING — naive filter drops ~1,000 counties in 2020+!
#    Use 3-pattern mode reconstruction instead. See ./references/mode-reconstruction.md
#    The single-line filter below is ONLY safe for single-year analysis on a state
#    known to have TOTAL rows (e.g., 2000-2016 data, or a confirmed TOTAL-only state).
longitudinal = df.filter(pl.col("mode") == "TOTAL")  # UNSAFE for 2020+ multi-state!

# 2. Remove non-candidate rows (UNDERVOTES, OVERVOTES, etc.)
candidates_only = df.filter(
    ~pl.col("candidate").is_in(["TOTAL VOTES CAST", "UNDERVOTES", "OVERVOTES", "SPOILED"])
)

# 3. Major party analysis — RECOMMENDED: use party column, not candidate name
#    Candidate names change across years (e.g., "DONALD TRUMP" vs "DONALD J TRUMP")
two_party = df.filter(pl.col("party").is_in(["DEMOCRAT", "REPUBLICAN"]))

# 4. Exclude Alaska 2004 anomaly
clean = df.filter(~((pl.col("state_po") == "AK") & (pl.col("year") == 2004)))

# 5. Exclude rows with null county_fips (for join operations)
joinable = df.filter(pl.col("county_fips").is_not_null())

Common Pitfalls

Pitfall	Issue	Solution
Cross-year mode mismatch	2000-2016 has only `TOTAL`; 2020/2024 have breakdowns. Mixing modes inflates counts	Always filter `mode == 'TOTAL'` for longitudinal analysis
Non-candidate rows	`UNDERVOTES`, `OVERVOTES`, `SPOILED`, `TOTAL VOTES CAST` appear as "candidates"	Filter out before computing candidate vote shares
Alaska 2004	District-level data with non-standard FIPS codes (2001-2099); vote counts overstated	Exclude AK 2004 or handle separately; do not join on county_fips
Null FIPS for joins	CT, ME, RI have null `county_fips` in some years; breaks joins	Use `state_po` + `county_name` as fallback join key
Kansas City MO FIPS	Uses non-standard FIPS 2938000 (not a real county FIPS)	Handle as special case in joins; Kansas City is an independent city
Empty string party/mode	2024 has `""` in party (501 rows) and mode (2,795 rows)	Treat as missing/undocumented; filter or investigate by state
Vote share > 100%	49 county-years where sum(candidatevotes) > totalvotes	Minor rounding; use caution with strict validation
Duplicate rows	83 exact duplicate rows exist in dataset	Deduplicate before analysis
FIPS zero-padding	Int64 → string without padding gives 4-digit codes for AR and other small-FIPS states	`pl.col("county_fips").cast(pl.Utf8).str.zfill(5)` before joins
Name-based party ID	Candidate names change across years ("DONALD TRUMP" vs "DONALD J TRUMP")	Always use `party` column, never `candidate` name
CT FIPS mismatch	2022+ Census TIGER uses CT planning regions, not legacy counties	Use 2020-vintage TIGER shapefiles for CT county joins
totalvotes duplication	`totalvotes` is repeated per candidate row; summing without dedup inflates by ~3-4x	Deduplicate to one row per (county_fips, year) before aggregating

Critical: Mode Column Behavior Change

WARNING: Naive mode == "TOTAL" filtering drops ~1,000 counties in 2020+ data. Multiple states report ONLY mode breakdowns (no TOTAL rows). A simple filter silently removes all their counties. Use 3-pattern mode reconstruction instead. See ./references/mode-reconstruction.md for the full code pattern and validation.

The mode column behavior changed significantly starting in 2020:

2000-2016: All rows have mode = 'TOTAL' (aggregate county totals only)
2020: 11 states report by voting method alongside TOTAL; 10 states have ONLY breakdowns (AR, AZ, GA, IA, KY, MD, NC, OK, SC, VA)
2024: Additional breakdown states; some have empty string mode (which may represent totals OR breakdowns depending on the state)

For any cross-year or multi-county analysis, use 3-pattern mode reconstruction:

Pattern 1: TOTAL present → keep TOTAL, drop breakdowns
Pattern 2: Only breakdowns, no TOTAL → sum candidatevotes across modes
Pattern 3: Empty-string mode = totals → reclassify after per-state verification

Empty-string detection must be per-state — NC 2024 empty-string rows are breakdowns (multiple per county-candidate), while other states' empty-string rows are totals (one per county-candidate). See ./references/mode-reconstruction.md for detection logic and code.

Related Data Sources

Source	Relationship	When to Use
Census/ACS	Join via `county_fips`	County demographics, population, income
SAIPE (`education-data-source-saipe`)	Join via `county_fips`	County poverty estimates (cross-domain)
CCD (`education-data-source-ccd`)	Join via `county_fips`	School district data (cross-domain)
MEDSL Precinct Returns	Finer geographic resolution	When county-level is insufficient
MEDSL Senate/House Returns	Same producer, different office	When analyzing down-ballot races

Note: This is the first election domain dataset in DAAF. Cross-domain joins with education data are possible via county_fips. No election-specific explorer or query skills exist yet.

Topic Index

Topic	Reference File
Column specifications	`./references/columns.md`
Column types and ranges	`./references/columns.md`
Party values and year coverage	`./references/coded-values.md`
Mode values and year behavior	`./references/coded-values.md`
Candidate name mapping	`./references/coded-values.md`
Non-candidate entries	`./references/coded-values.md`
Complete encoding tables	`./references/variable-definitions.md`
Null county_fips patterns	`./references/quality-notes.md`
Alaska 2004 anomaly	`./references/quality-notes.md`
Kansas City MO FIPS	`./references/quality-notes.md`
Duplicate rows	`./references/quality-notes.md`
Null candidatevotes	`./references/quality-notes.md`
Per-state data sources	`./references/quality-notes.md`
Missing votes flags	`./references/quality-notes.md`
Mode reconstruction (3-pattern)	`./references/mode-reconstruction.md`
States without TOTAL rows	`./references/mode-reconstruction.md`
Empty-string mode detection	`./references/mode-reconstruction.md`
Row count estimation by year	`./references/mode-reconstruction.md`
FIPS zero-padding for joins	`./references/columns.md`
AR FIPS contamination (Sharp/St. Francis)	`./references/quality-notes.md`
CT geography mismatch (2022+)	`./references/quality-notes.md`
Party-based identification (best practice)	`./references/coded-values.md`
totalvotes deduplication	`./references/variable-definitions.md`
Preliminary interpretations	`./references/interpretations.md`
Data profiling scripts	`./scripts/`

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County Presidential Data Source Reference

Prerequisites

What is the MEDSL County Presidential Returns Dataset?

Reference File Structure

Decision Trees

What analysis do I need?

Is this a data quality issue?

Quick Reference: Election Variables

Party Values by Year

Mode Values by Year

Key Identifiers

Missing Data Codes

Non-Candidate Entries in candidate Column

Data Access

Dataset Paths

Codebooks

Example Fetch

Filtering

Common Pitfalls

Critical: Mode Column Behavior Change

Related Data Sources

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