advanced-evaluation

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# Advanced Evaluation

This skill covers production-grade techniques for evaluating LLM outputs using LLMs as judges. It synthesizes research from academic papers, industry practices, and practical implementation experience into actionable patterns for building reliable evaluation systems.

**Key insight**: LLM-as-a-Judge is not a single technique but a family of approaches, each suited to different evaluation contexts. Choosing the right approach and mitigating known biases is the core competency this skill develops.

## When to Use
Activate this skill when:

- Building automated evaluation pipelines for LLM outputs
- Comparing multiple model responses to select the best one
- Establishing consistent quality standards across evaluation teams
- Debugging evaluation systems that show inconsistent results
- Designing A/B tests for prompt or model changes
- Creating rubrics for human or automated evaluation
- Analyzing correlation between automated and human judgments

## Core Concepts

### The Evaluation Taxonomy

Evaluation approaches fall into two primary categories with distinct reliability profiles:

**Direct Scoring**: A single LLM rates one response on a defined scale.
- Best for: Objective criteria (factual accuracy, instruction following, toxicity)
- Reliability: Moderate to high for well-defined criteria
- Failure mode: Score calibration drift, inconsistent scale interpretation

**Pairwise Comparison**: An LLM compares two responses and selects the better one.
- Best for: Subjective preferences (tone, style, persuasiveness)
- Reliability: Higher than direct scoring for preferences
- Failure mode: Position bias, length bias

Research from the MT-Bench paper (Zheng et al., 2023) establishes that pairwise comparison achieves higher agreement with human judges than direct scoring for preference-based evaluation, while direct scoring remains appropriate for objective criteria with clear ground truth.

### The Bias Landscape

LLM judges exhibit systematic biases that must be actively mitigated:

**Position Bias**: First-position responses receive preferential treatment in pairwise comparison. Mitigation: Evaluate twice with swapped positions, use majority vote or consistency check.

**Length Bias**: Longer responses are rated higher regardless of quality. Mitigation: Explicit prompting to ignore length, length-normalized scoring.

**Self-Enhancement Bias**: Models rate their own outputs higher. Mitigation: Use different models for generation and evaluation, or acknowledge limitation.

**Verbosity Bias**: Detailed explanations receive higher scores even when unnecessary. Mitigation: Criteria-specific rubrics that penalize irrelevant detail.

**Authority Bias**: Confident, authoritative tone rated higher regardless of accuracy. Mitigation: Require evidence citation, fact-checking layer.

### Metric Selection Framework

Choose metrics based on the evaluation task structure:

| Task Type | Primary Metrics | Secondary Metrics |
|-----------|-----------------|-------------------|
| Binary classification (pass/fail) | Recall, Precision, F1 | Cohen's κ |
| Ordinal scale (1-5 rating) | Spearman's ρ, Kendall's τ | Cohen's κ (weighted) |
| Pairwise preference | Agreement rate, Position consistency | Confidence calibration |
| Multi-label | Macro-F1, Micro-F1 | Per-label precision/recall |

The critical insight: High absolute agreement matters less than systematic disagreement patterns. A judge that consistently disagrees with humans on specific criteria is more problematic than one with random noise.

## Evaluation Approaches

### Direct Scoring Implementation

Direct scoring requires three components: clear criteria, a calibrated scale, and structured output format.

**Criteria Definition Pattern**:
```
Criterion: [Name]
Description: [What this criterion measures]
Weight: [Relative importance, 0-1]
```

**Scale Calibration**:
- 1-3 scales: Binary with neutral option, lowest cognitive load
- 1-5 scales: Standard Likert, good balance of granularity and reliability
- 1-10 scales: High granularity but harder to calibrate, use only with detailed rubrics

**Prompt Structure for Direct Scoring**:
```
You are an expert evaluator assessing response quality.

## Task
Evaluate the following response against each criterion.

## Original Prompt
{prompt}

## Response to Evaluate
{response}

## Criteria
{for each criterion: name, description, weight}

## Instructions
For each criterion:
1. Find specific evidence in the response
2. Score according to the rubric (1-{max} scale)
3. Justify your score with evidence
4. Suggest one specific improvement

## Output Format
Respond with structured JSON containing scores, justifications, and summary.
```

**Chain-of-Thought Requirement**: All scoring prompts must require justification before the score. Research shows this improves reliability by 15-25% compared to score-first approaches.

### Pairwise Comparison Implementation

Pairwise comparison is inherently more reliable for preference-based evaluation but requires bias mitigation.

**Position Bias Mitigation Protocol**:
1. First pass: Response A in first position, Response B in second
2. Second pass: Response B in first position, Response A in second
3. Consistency check: If passes disagree, return TIE with reduced confidence
4. Final verdict: Consistent winner with averaged confidence

From wellingtonspdev/skills-wsp, MIT.

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