Ground Truth Management

What is Ground Truth?

Definition: Correct answers for evaluation - human-verified data that serves as the gold standard for measuring AI performance.

Example

Question: "What is the capital of France?"
Ground Truth: "Paris"

AI Answer: "Paris" → Correct ✓
AI Answer: "Lyon" → Incorrect ✗

---

Why Ground Truth Matters

Measure Accuracy Objectively

Without ground truth: "This answer seems good" (subjective)
With ground truth: "Accuracy: 85%" (objective)

Train and Validate Models

Training: Learn from ground truth examples
Validation: Measure performance on ground truth test set

Regression Testing

Before change: Accuracy 90%
After change: Accuracy 85%
→ Regression detected!

Benchmarking

Model A: 90% accuracy on ground truth
Model B: 85% accuracy on ground truth
→ Model A is better

---

Types of Ground Truth

Exact Match: Single Correct Answer

{
  "question": "What is 2+2?",
  "answer": "4"
}

Multiple Acceptable Answers

{
  "question": "What is the capital of France?",
  "acceptable_answers": ["Paris", "paris", "PARIS", "The capital is Paris"]
}

Rubric-Based: Quality Scale

{
  "question": "Summarize this article",
  "rubric": {
    "1": "Poor summary, missing key points",
    "3": "Adequate summary, covers main points",
    "5": "Excellent summary, concise and comprehensive"
  }
}

Human Preference: Comparison Rankings

{
  "question": "Which answer is better?",
  "answer_a": "Paris is the capital of France.",
  "answer_b": "The capital of France is Paris, a city of 2.1 million people.",
  "preference": "B",
  "reasoning": "More informative"
}

---

Creating Ground Truth

Manual Annotation (Humans Label)

Process:
1. Collect examples (questions, documents, images)
2. Human annotators label each
3. Quality control (review annotations)
4. Store in dataset

Expert Review (For Specialized Domains)

Medical: Doctors annotate
Legal: Lawyers annotate
Technical: Engineers annotate

Higher quality but more expensive

Crowdsourcing (Amazon MTurk)

Pros:
- Fast (many workers)
- Cheap ($0.10-1.00 per annotation)

Cons:
- Variable quality
- Need quality control

Synthetic Generation (For Some Tasks)

LLM-generated questions + answers
Careful validation needed
Good for scale, risky for quality
Use for augmentation, not sole source

---

Ground Truth Dataset Structure

Input (Question, Document, Image)

{
  "input": {
    "type": "question",
    "text": "What is the capital of France?"
  }
}

Expected Output (Answer, Label, Summary)

{
  "expected_output": {
    "type": "answer",
    "text": "Paris",
    "acceptable_variants": ["paris", "PARIS"]
  }
}

Metadata (Difficulty, Category, Source)

{
  "metadata": {
    "difficulty": "easy",
    "category": "geography",
    "source": "wikipedia",
    "language": "en"
  }
}

Annotation Info (Who, When, Confidence)

{
  "annotation": {
    "annotator_id": "annotator_123",
    "timestamp": "2024-01-15T10:00:00Z",
    "confidence": 0.95,
    "time_spent_seconds": 30
  }
}

Complete Example:

{
  "id": "example_001",
  "input": {
    "type": "question",
    "text": "What is the capital of France?"
  },
  "expected_output": {
    "type": "answer",
    "text": "Paris",
    "acceptable_variants": ["paris", "PARIS", "The capital is Paris"]
  },
  "metadata": {
    "difficulty": "easy",
    "category": "geography",
    "source": "wikipedia",
    "language": "en"
  },
  "annotation": {
    "annotator_id": "annotator_123",
    "timestamp": "2024-01-15T10:00:00Z",
    "confidence": 0.95
  }
}

---

Annotation Guidelines

Clear Instructions

# Annotation Guidelines

## Task
Label whether the answer is correct.

## Instructions
1. Read the question carefully
2. Read the answer
3. Determine if answer is factually correct
4. Mark as "Correct" or "Incorrect"

## Examples
Question: "What is 2+2?"
Answer: "4"
Label: Correct

Question: "What is 2+2?"
Answer: "5"
Label: Incorrect

Examples (Good and Bad)

## Good Example
Question: "What is the capital of France?"
Answer: "Paris"
Label: Correct
Reasoning: Factually accurate and directly answers question

## Bad Example
Question: "What is the capital of France?"
Answer: "France is a country in Europe"
Label: Incorrect
Reasoning: Doesn't answer the question

Edge Case Handling

## Edge Cases

### Partially Correct
Question: "What are the capitals of France and Germany?"
Answer: "Paris"
Label: Partially Correct (missing Germany)

### Ambiguous Question
Question: "What is the best programming language?"
Label: N/A - Subjective question, no single correct answer

### No Answer in Context
Question: "What is the population of Paris?"
Context: "Paris is the capital of France."
Label: "Cannot be determined from context"

Consistency Checks

## Consistency Rules

1. Same question → Same answer
2. Synonyms are acceptable ("car" = "automobile")
3. Case-insensitive ("Paris" = "paris")
4. Extra details are OK ("Paris" vs "Paris, France")

---

Quality Control

Multiple Annotators Per Example

Each example labeled by 3 annotators
Majority vote determines final label
Catches individual annotator errors

Inter-Annotator Agreement (IAA)

Measure: Do annotators agree?
Metric: Cohen's Kappa (κ)
Target: κ > 0.7 (good agreement)

Gold Standard Subset (Known Answers)

10% of examples have known correct labels
Mix into annotation tasks
Measure annotator accuracy on gold standard
Remove low-quality annotators

Spot Checks by Experts

Expert reviews 10% of annotations
Validates quality
Identifies systematic errors

---

Inter-Annotator Agreement

Kappa Score (Cohen's κ)

from sklearn.metrics import cohen_kappa_score

annotator1 = [1, 0, 1, 1, 0]  # Labels from annotator 1
annotator2 = [1, 0, 1, 0, 0]  # Labels from annotator 2

kappa = cohen_kappa_score(annotator1, annotator2)
print(f"Kappa: {kappa:.2f}")

# Interpretation:
# κ < 0.4: Poor agreement
# κ 0.4-0.6: Moderate agreement
# κ 0.6-0.8: Good agreement
# κ > 0.8: Excellent agreement

Fleiss' κ (Multiple Annotators)

from statsmodels.stats.inter_rater import fleiss_kappa

# 3 annotators, 5 examples
# Each row: [count_label_0, count_label_1]
data = [
    [0, 3],  # Example 1: All 3 annotators chose label 1
    [1, 2],  # Example 2: 1 chose 0, 2 chose 1
    [3, 0],  # Example 3: All 3 chose label 0
    [2, 1],  # Example 4: 2 chose 0, 1 chose 1
    [0, 3],  # Example 5: All 3 chose label 1
]

kappa = fleiss_kappa(data)
print(f"Fleiss' Kappa: {kappa:.2f}")

Percentage Agreement

def percentage_agreement(annotator1, annotator2):
    agreements = sum(a == b for a, b in zip(annotator1, annotator2))
    total = len(annotator1)
    return agreements / total

agreement = percentage_agreement(annotator1, annotator2)
print(f"Agreement: {agreement:.1%}")

Target: >0.7 (Good Agreement)

If κ < 0.7:
1. Review annotation guidelines (unclear?)
2. Provide more examples
3. Train annotators
4. Simplify task

---

Resolving Disagreements

Majority Vote

def majority_vote(labels):
    from collections import Counter
    counts = Counter(labels)
    majority_label = counts.most_common(1)[0][0]
    return majority_label

# 3 annotators
labels = [1, 1, 0]  # Two say 1, one says 0
final_label = majority_vote(labels)  # 1

Expert Adjudication

If no majority (e.g., 1, 0, 2):
→ Expert reviews and decides

Discussion and Consensus

Annotators discuss disagreement
Reach consensus
Update guidelines if needed

Update Guidelines

If systematic disagreements:
→ Guidelines unclear
→ Update and re-annotate

---

Ground Truth for Different Tasks

Classification: Category Labels

{
  "text": "This product is amazing!",
  "label": "positive"
}

Q&A: Correct Answers + Acceptable Variants

{
  "question": "What is the capital of France?",
  "answer": "Paris",
  "acceptable_variants": ["paris", "PARIS", "The capital is Paris"]
}

Summarization: Reference Summaries

{
  "document": "Long article text...",
  "reference_summary": "Concise summary of key points"
}

RAG: Question + Context + Answer

{
  "question": "What is the capital of France?",
  "context": "Paris is the capital and largest city of France.",
  "answer": "Paris",
  "relevant_chunks": ["Paris is the capital and largest city of France."]
}

Generation: Multiple Acceptable Outputs

{
  "prompt": "Write a haiku about spring",
  "acceptable_outputs": [
    "Cherry blossoms bloom\nGentle breeze carries petals\nSpring has arrived now",
    "Flowers start to bloom\nBirds sing in the morning light\nSpring is here at last"
  ]
}

---

Dataset Size

Evaluation Set: 100-1000 Examples (Representative)

Purpose: Quick evaluation during development
Size: 100-1000 examples
Quality: High (manually curated)
Coverage: Representative of production

Test Set: 500-5000 Examples (Comprehensive)

Purpose: Final evaluation before deployment
Size: 500-5000 examples
Quality: High (gold standard)
Coverage: Comprehensive (all categories, edge cases)

Quality > Quantity

Better: 100 high-quality examples
Worse: 1000 low-quality examples

Cover Edge Cases

Include:
- Common cases (80%)
- Edge cases (15%)
- Adversarial cases (5%)

---

Dataset Maintenance

Version Control (Like Code)

# Git for dataset versioning
git init
git add dataset.jsonl
git commit -m "Initial dataset v1.0"

# Tag versions
git tag v1.0

# Update dataset
git add dataset.jsonl
git commit -m "Added 100 new examples"
git tag v1.1

Regular Updates (New Examples)

Monthly: Add 50-100 new examples
Quarterly: Major update (500+ examples)

Remove Outdated Examples

Examples that are:
- No longer relevant
- Incorrect (facts changed)
- Duplicates

Track Changes (Changelog)

# Dataset Changelog

## v1.2 (2024-02-01)
- Added 100 new examples (geography category)
- Removed 20 outdated examples
- Fixed 5 incorrect labels

## v1.1 (2024-01-01)
- Added 50 new examples (science category)
- Updated annotation guidelines

## v1.0 (2023-12-01)
- Initial release (500 examples)

---

Stratified Sampling

Balance by Difficulty

Easy: 40%
Medium: 40%
Hard: 20%

Balance by Category

Geography: 25%
Science: 25%
History: 25%
Math: 25%

Include Edge Cases

Common cases: 80%
Edge cases: 15%
Adversarial: 5%

Representative of Production

Sample from actual production queries
Ensures dataset matches real usage

---

Synthetic Ground Truth

LLM-Generated Questions + Answers

def generate_synthetic_qa(document):
    prompt = f"""
    Document: {document}
    
    Generate 5 question-answer pairs based on this document.
    
    Format:
    Q1: [question]
    A1: [answer]
    ...
    """
    
    response = llm.generate(prompt)
    qa_pairs = parse_qa_pairs(response)
    return qa_pairs

Careful Validation Needed

LLM-generated data can have:
- Hallucinations
- Incorrect facts
- Biased questions

→ Always validate with humans

Good for Scale, Risky for Quality

Pros: Can generate 1000s quickly
Cons: Quality varies, needs validation

Use for Augmentation, Not Sole Source

Strategy:
- 80% human-annotated (high quality)
- 20% synthetic (validated)

---

Domain-Specific Ground Truth

Medical: Expert Annotations

Annotators: Licensed doctors
Cost: $50-100 per hour
Quality: Very high
Use case: Medical diagnosis, treatment recommendations

Legal: Lawyer Review

Annotators: Licensed lawyers
Cost: $100-300 per hour
Quality: Very high
Use case: Legal document analysis, case law

Technical: Engineer Verification

Annotators: Senior engineers
Cost: $50-150 per hour
Quality: High
Use case: Code review, technical Q&A

---

Ground Truth Storage

JSON/JSONL Files

{"id": "1", "question": "What is 2+2?", "answer": "4"}
{"id": "2", "question": "Capital of France?", "answer": "Paris"}

Database (PostgreSQL, MongoDB)

CREATE TABLE ground_truth (
  id UUID PRIMARY KEY,
  question TEXT NOT NULL,
  answer TEXT NOT NULL,
  category VARCHAR(50),
  difficulty VARCHAR(20),
  created_at TIMESTAMP DEFAULT NOW()
);

Version Control (Git)

git add dataset/
git commit -m "Update ground truth dataset"
git push

Cloud Storage (S3 + Versioning)

# Upload to S3 with versioning
aws s3 cp dataset.jsonl s3://my-bucket/ground-truth/v1.0/dataset.jsonl
aws s3api put-bucket-versioning --bucket my-bucket --versioning-configuration Status=Enabled

---

Ground Truth for RAG

Structure:

{
  "question": "What is the capital of France?",
  "expected_answer": "Paris",
  "relevant_document_chunks": [
    "Paris is the capital and largest city of France."
  ],
  "evaluation_criteria": {
    "faithfulness": "Answer must be grounded in context",
    "relevance": "Answer must directly address question",
    "completeness": "Answer should mention Paris"
  }
}

---

Evaluation with Ground Truth

Exact Match Accuracy

def exact_match(predicted, ground_truth):
    return predicted.strip().lower() == ground_truth.strip().lower()

accuracy = sum(exact_match(p, gt) for p, gt in zip(predicted, ground_truth)) / len(predicted)

F1 Score (For Overlapping Spans)

def f1_score(predicted, ground_truth):
    pred_tokens = set(predicted.lower().split())
    gt_tokens = set(ground_truth.lower().split())
    
    common = pred_tokens & gt_tokens
    if len(pred_tokens) == 0 or len(gt_tokens) == 0:
        return 0
    
    precision = len(common) / len(pred_tokens)
    recall = len(common) / len(gt_tokens)
    
    if precision + recall == 0:
        return 0
    
    f1 = 2 * (precision * recall) / (precision + recall)
    return f1

BLEU/ROUGE (For Generation)

from nltk.translate.bleu_score import sentence_bleu

reference = [["Paris", "is", "the", "capital"]]
candidate = ["Paris", "is", "the", "capital"]

bleu = sentence_bleu(reference, candidate)

Semantic Similarity (Embedding Distance)

from sentence_transformers import SentenceTransformer
from sklearn.metrics.pairwise import cosine_similarity

model = SentenceTransformer('all-MiniLM-L6-v2')

emb1 = model.encode("Paris is the capital of France")
emb2 = model.encode("The capital of France is Paris")

similarity = cosine_similarity([emb1], [emb2])[0][0]

---

Continuous Ground Truth

Production Feedback (User Thumbs Up/Down)

# Log user feedback
feedback = {
    "question": "What is the capital of France?",
    "answer": "Paris",
    "user_feedback": "thumbs_up",
    "timestamp": "2024-01-15T10:00:00Z"
}

# Add to ground truth if positive
if feedback["user_feedback"] == "thumbs_up":
    add_to_ground_truth(feedback["question"], feedback["answer"])

Human Review of Flagged Outputs

User flags answer as incorrect
→ Human reviews
→ If incorrect, add correct answer to ground truth
→ If correct, keep as is

Incrementally Add to Dataset

Monthly: Review 100 flagged examples
Add 50 to ground truth
Update dataset version

---

Tools

Annotation: Label Studio, Prodigy, CVAT

Label Studio:

pip install label-studio
label-studio start
# Open http://localhost:8080

Prodigy:

pip install prodigy
prodigy textcat.manual dataset_name source.jsonl --label positive,negative

Management: DVC (Data Version Control)

pip install dvc
dvc init
dvc add dataset.jsonl
git add dataset.jsonl.dvc .gitignore
git commit -m "Add dataset"
dvc push

Storage: S3, GCS, Local Files

See "Ground Truth Storage" section

---

Summary

Ground Truth: Correct answers for evaluation

Why:

• Measure accuracy objectively
• Train/validate models
• Regression testing
• Benchmarking

Types:

• Exact match
• Multiple acceptable answers
• Rubric-based
• Human preference

Creating:

• Manual annotation
• Expert review
• Crowdsourcing
• Synthetic (with validation)

Quality Control:

• Multiple annotators
• Inter-annotator agreement (κ > 0.7)
• Gold standard subset
• Expert spot checks

Dataset Size:

• Eval: 100-1000 (representative)
• Test: 500-5000 (comprehensive)
• Quality > quantity

Maintenance:

• Version control (Git)
• Regular updates
• Remove outdated
• Changelog

Tools:

• Annotation: Label Studio, Prodigy
• Management: DVC
• Storage: S3, GCS, Git