Agent Skills: Advanced Evaluation

Advanced Evaluation

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 Activate

• Building LLM-as-judge systems 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 specifically for LLM or human/LLM hybrid judges
• Analyzing correlation between automated and human judgments

Do not activate this skill for adjacent work owned by other skills:

• General deterministic checks, regression suites, production quality gates, or outcome metrics: evaluation.
• Tool API contracts for evaluation tools: tool-design.

Core Concepts

The Evaluation Taxonomy

Select between two primary approaches based on whether ground truth exists:

Direct Scoring — Use when objective criteria exist (factual accuracy, instruction following, toxicity). A single LLM rates one response on a defined scale. Achieves moderate-to-high reliability for well-defined criteria. Watch for score calibration drift and inconsistent scale interpretation.

Pairwise Comparison — Use for subjective preferences (tone, style, persuasiveness). An LLM compares two responses and selects the better one. Pairwise methods often correlate better with human preference than open-ended direct scoring for subjective tasks (claim-advanced-evaluation-position-swap). Watch for position bias and length bias.

The Bias Landscape

Mitigate these systematic biases in every evaluation system:

Position Bias: First-position responses get preferential treatment. Mitigate by evaluating twice with swapped positions, then apply majority vote or consistency check.

Length Bias: Longer responses score higher regardless of quality. Mitigate by explicitly prompting to ignore length and applying length-normalized scoring.

Self-Enhancement Bias: Models rate their own outputs higher. Mitigate by using different models for generation and evaluation.

Verbosity Bias: Excessive detail scores higher even when unnecessary. Mitigate with criteria-specific rubrics that penalize irrelevant detail.

Authority Bias: Confident tone scores higher regardless of accuracy. Mitigate by requiring evidence citation and adding a fact-checking layer.

Metric Selection Framework

Match metrics to the evaluation task structure:

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

Prioritize systematic disagreement patterns over absolute agreement rates because a judge that consistently disagrees with humans on specific criteria is more problematic than one with random noise.

Evaluation Approaches

Direct Scoring Implementation

Build direct scoring with 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 — Choose scale granularity based on rubric detail:

• 1-3: Binary with neutral option, lowest cognitive load
• 1-5: Standard Likert, best balance of granularity and reliability
• 1-10: Use only with detailed per-level rubrics because calibration is harder

Require evidence before the score in scoring prompts so the judge must anchor its decision in observable output features before emitting a number. See references/examples.md (§ Direct Scoring Prompt Template) for the full prompt.

Pairwise Comparison Implementation

Apply position bias mitigation in every pairwise evaluation:

1. Run deterministic pre-checks first: both candidates must satisfy the same schema, source-evidence requirements, and scope constraints.
2. First judge pass: Response A in first position, Response B in second.
3. Second judge pass: Response B in first position, Response A in second.
4. Consistency check: If passes disagree, return TIE with reduced confidence.
5. Final verdict: Consistent winner with averaged confidence and explicit tie-breaker rationale.

Confidence Calibration — map confidence to position consistency: both passes agree → confidence = average of individual confidences; passes disagree → confidence = 0.5, verdict = TIE. See references/examples.md (§ Pairwise Comparison Prompt Template) for the full prompt.

Rubric Generation

Generate rubrics to reduce evaluation variance compared to open-ended scoring. Treat exact variance reduction as workload-specific unless measured on the target eval set.

Include these rubric components:

1. Level descriptions: Clear boundaries for each score level
2. Characteristics: Observable features that define each level
3. Examples: Representative text for each level (optional but valuable)
4. Edge cases: Guidance for ambiguous situations
5. Scoring guidelines: General principles for consistent application

Set strictness calibration for the use case:

• Lenient: Lower passing bar, appropriate for encouraging iteration
• Balanced: Typical production expectations
• Strict: High standards for safety-critical or high-stakes evaluation

Adapt rubrics to the domain — use domain-specific terminology. A code readability rubric mentions variables, functions, and comments. A medical accuracy rubric references clinical terminology and evidence standards.

Practical Guidance

Evaluation Pipeline Design

Build production evaluation systems with these layers: Criteria Loader (rubrics + weights) -> Primary Scorer (direct or pairwise) -> Bias Mitigation (position swap, etc.) -> Confidence Scoring (calibration) -> Output (scores + justifications + confidence). See Evaluation Pipeline Diagram for the full visual layout.

Decision Framework: Direct vs. Pairwise

Apply this decision tree:

Is there an objective ground truth?
+-- Yes -> Direct Scoring
|   Examples: factual accuracy, instruction following, format compliance
|
+-- No -> Is it a preference or quality judgment?
    +-- Yes -> Pairwise Comparison
    |   Examples: tone, style, persuasiveness, creativity
    |
    +-- No -> Consider reference-based evaluation
        Examples: summarization (compare to source), translation (compare to reference)

Scaling Evaluation

For high-volume evaluation, apply one of these strategies:

1. Panel of LLMs (PoLL): Use multiple models as judges and aggregate votes to reduce individual model bias. More expensive but more reliable for high-stakes decisions.

2. Hierarchical evaluation: Use a fast cheap model for screening and an expensive model for edge cases. Requires calibration of the screening threshold.

3. Human-in-the-loop: Automate clear cases and route low-confidence decisions to human review. Design feedback loops to improve automated evaluation over time.

Examples

Three worked examples — direct scoring for factual accuracy, pairwise comparison with position swap, and rubric generation — are in references/examples.md (§ Example 1-3).

Guidelines

1. Always require evidence before scores - Evidence-first prompts make judgments easier to audit and reduce ungrounded numeric scoring

2. Always swap positions in pairwise comparison - Single-pass comparison is corrupted by position bias

3. Match scale granularity to rubric specificity - Don't use 1-10 without detailed level descriptions

4. Separate objective and subjective criteria - Use direct scoring for objective, pairwise for subjective

5. Include confidence scores - Calibrate to position consistency and evidence strength

6. Define edge cases explicitly - Ambiguous situations cause the most evaluation variance

7. Use domain-specific rubrics - Generic rubrics produce generic evaluations

8. Validate against human judgments - Automated evaluation is only valuable if it correlates with human assessment

9. Monitor for systematic bias - Track disagreement patterns by criterion, response type, model

10. Design for iteration - Evaluation systems improve with feedback loops

Gotchas

1. Scoring without justification: Scores lack grounding and are difficult to debug. Always require evidence-based justification before the score.

2. Single-pass pairwise comparison: Position bias corrupts results when positions are not swapped. Always evaluate twice with swapped positions and check consistency.

3. Overloaded criteria: Criteria that measure multiple things at once produce unreliable scores. Enforce one criterion = one measurable aspect.

4. Missing edge case guidance: Evaluators handle ambiguous cases inconsistently without explicit instructions. Include edge cases in rubrics with clear resolution rules.

5. Ignoring confidence calibration: High-confidence wrong judgments are worse than low-confidence ones. Calibrate confidence to position consistency and evidence strength.

6. Rubric drift: Rubrics become miscalibrated as quality standards evolve or model capabilities improve. Schedule periodic rubric reviews and re-anchor score levels against fresh human-annotated examples.

7. Evaluation prompt sensitivity: Minor wording changes in evaluation prompts can cause material score swings. Version-control evaluation prompts and run regression tests before deploying prompt changes.

8. Uncontrolled length bias: Longer responses systematically score higher even when conciseness is preferred. Add explicit length-neutrality instructions to evaluation prompts and validate with length-controlled test pairs.

Integration

This skill owns judge design and bias mitigation. Adjacent skills own broader quality gates and infrastructure:

• evaluation: general deterministic checks, regression suites, quality gates, and production monitoring.
• context-fundamentals: context structure for judge prompts.
• tool-design: schemas and error handling for evaluation tools.
• context-optimization: token and latency efficiency for high-volume evals.

References

Internal reference:

• LLM-as-Judge Implementation Patterns - Read when: building an evaluation pipeline from scratch or integrating LLM judges into CI/CD
• Bias Mitigation Techniques - Read when: evaluation results show inconsistent or suspicious scoring patterns
• Metric Selection Guide - Read when: choosing statistical metrics to validate evaluation reliability
• Evaluation Pipeline Diagram - Read when: designing the architecture of a multi-stage evaluation system
• Prompt Templates & Worked Examples - Read when: writing direct scoring or pairwise comparison prompts, or reviewing full worked examples

External research:

• Eugene Yan: Evaluating the Effectiveness of LLM-Evaluators - Read when: surveying the state of the art in LLM evaluation
• Judging LLM-as-a-Judge (Zheng et al., 2023) - Read when: understanding position bias and MT-Bench methodology
• G-Eval paper (Liu et al., 2023) - Read when: implementing chain-of-thought evaluation scoring
• Large Language Models are not Fair Evaluators (Wang et al., 2023) - Read when: diagnosing systematic bias in evaluation outputs

Related skills in this collection:

• evaluation - Foundational evaluation concepts
• context-fundamentals - Context structure for evaluation prompts
• tool-design - Building evaluation tools