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Introduction to Model Evaluation

Evaluation is a critical step in developing and deploying language models. It helps us understand how well our models perform across different capabilities and identify areas for improvement. This unit focuses on benchmark evaluation approaches to comprehensively assess your smol model.

> We are already using evaluation to submit models to the course leaderboard. In this unit we will explore evaluation in more detail and use what we learn to evaluate our models and submit them to the leaderboard.

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Why Evaluation Matters

When we train or fine-tune a language model, we need systematic ways to measure its quality and performance. Evaluation helps us:

- Compare models objectively so that we can understand how different models or training approaches perform. Use standardized metrics to compare different models or training approaches
- Identify strengths and weaknesses so that we can understand where our model excels and where it needs improvement
- Track progress so that we can monitor improvements across training iterations
- Ensure deployment readiness so that we can verify that our model meets performance requirements before production use
- Detect regressions so that we can catch performance degradation when making changes

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Tool of choice: LightEval

We’ll use `lighteval`, a powerful evaluation library developed by Hugging Face that integrates seamlessly with the Hugging Face ecosystem. LightEval provides:

- Access to standard benchmarks like MMLU, TruthfulQA, BBH, and GSM8K
- Flexible framework for creating custom evaluation tasks
- Efficient batch processing and parallelization with vLLM backend
- Integration with the Hugging Face model Hub
- Reproducible evaluation pipelines

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Installation and Setup

To get started with LightEval and vLLM, install the required packages:

    # Install LightEval with vLLM support
    pip install lighteval[vllm]

    # Or install separately
    pip install lighteval
    pip install vllm

vLLM provides significant speed improvements for evaluation by:

- Optimized attention mechanisms
- Efficient memory management
- Automatic batching and parallelization
- Support for tensor and data parallelism across multiple GPUs

> There are certainly great alternatives to LightEval, which users might prefer to use, but for the purposes of this course we will stick with LightEval. Mainly because it offers a reproducible and complete set of evaluation tasks and metrics for all major benchmarks.

> Some alternatives that we might explore later in the course are:

> - lm-evaluation-harness
> - OpenBench

For a deeper dive into evaluation concepts and best practices, check out the Evaluation Guidebook.

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Types of Evaluation

To start, we will explore the two main types of evaluation: automatic benchmarks and domain-specific evaluation.

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1. Automatic Benchmarks

Standard benchmarks provide a common ground for model comparison. They test various capabilities:

- General Knowledge: For example, MMLU tests knowledge across 57 subjects
- Truthfulness: For example, TruthfulQA evaluates tendency to reproduce misconceptions
- Reasoning: For example, BBH and GSM8K test logical thinking and mathematical problem-solving
- Language Understanding: For example, WinoGrande tests common sense reasoning

While these benchmarks are valuable for baseline comparisons, they have limitations:

- May not reflect real-world performance where models are deployed.
- Can be gamed through overfitting and leaking data.
- Don’t capture domain-specific or user-specific requirements.

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2. Domain-Specific Evaluation

Custom evaluations tailored to your use case provide more relevant insights:

- Test actual tasks your model will perform in a real-world setting.
- Use real examples from your domain.
- Implement metrics that matter for your application.
- Evaluate edge cases and failure modes.

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3. Multi-Layered Evaluation Strategy

A comprehensive approach combines multiple evaluation methods:

1. Automated metrics for quick feedback during development
2. Human evaluation for nuanced quality assessment
3. Domain expert review for specialized applications
4. A/B testing in controlled production environments

During training, you will use automatic benchmarks to evaluate your model’s performance and make modeling or parameter decisions based on the results. However, during deployment, you will need to use domain-specific evaluation to ensure that your model is performing as expected.

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Understanding Evaluation Metrics

Common metrics you’ll encounter:

- Accuracy: Percentage of correct predictions
- F1 Score: Harmonic mean of precision and recall
- Perplexity: How well the model predicts text
- BLEU/ROUGE: Text generation quality metrics
- Custom metrics: Domain-specific measurements

Each metric has strengths and limitations. Choose metrics that align with your application’s requirements.

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Best Practices

1. Start with relevant benchmarks: Establish baselines using standard benchmarks related to your domain
2. Develop custom evaluations early: Don’t wait until the end to create domain-specific tests
3. Version control everything: Track evaluation datasets, code, and results
4. Document your methodology: Record assumptions, limitations, and design decisions
5. Iterate based on findings: Use evaluation results to guide model improvements

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What’s Next

In the following sections, we’ll dive deeper into:

- Running automatic benchmarks with LightEval
- Creating custom evaluation tasks and metrics
- Building comprehensive evaluation pipelines
- Hands-on exercises to practice these concepts

Let’s start by exploring how to use standard benchmarks effectively!

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