# Eval Observability — Variance and Drift
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Variance and drift checks detect when evaluation scores are **unstable across runs** or when **semantic meaning slowly shifts** without clear boundary failures.
These probes prevent "false confidence" in benchmarks by catching hidden instability.
---
## Why variance and drift matter
- **Variance**: Scores fluctuate heavily depending on seed, paraphrase, or retriever order. Averages hide the volatility.
- **Drift**: Performance declines slowly across sessions, data refreshes, or version bumps. Looks fine short-term but collapses long-term.
- **Silent regressions**: Systems pass local tests but fail in production due to unmonitored entropy rise.
---
## Acceptance targets
- **Variance (σ/μ)** ≤ 0.15 across 3 seeds and 3 paraphrases.
- **Drift slope**: Δscore per batch ≤ 0.02 absolute over 5+ eval windows.
- **No monotonic downward slope** longer than 3 consecutive windows.
- **Drift alerts** fire if ΔS average increases ≥ 0.10 compared to gold anchors.
---
## Detection workflow
1. **Collect runs across seeds**
- At least 3 seeds, 3 paraphrases.
- Log ΔS, λ, coverage, citations.
2. **Compute variance**
- Calculate σ/μ for each metric.
- High variance = unstable eval → rerun with schema locks.
3. **Track drift over time**
- Compare eval batch N vs N-1.
- Plot moving average.
- Alert if slope exceeds tolerance.
4. **Root-cause analysis**
- If variance high → check retriever metrics, random seeding, rerankers.
- If drift detected → audit embeddings, re-chunk, verify data refresh.
---
## Common pitfalls
- **Single-run evals**: Hides high variance. Always run multi-seed.
- **Averages without spread**: Mean looks fine, variance reveals collapse.
- **Ignoring slow drift**: Short tests OK, but 1–2 weeks later accuracy dies.
- **Cross-store drift**: One vector DB stable, another drifts. Must track both.
---
## Example reporting schema
```json
{
"metric": "ΔS",
"seed_runs": [0.38, 0.42, 0.44],
"variance_ratio": 0.14,
"drift_slope": +0.03,
"alert": true
}
````
---
## Fix modules to open
* **Retriever instability** → [Rerankers](https://github.com/onestardao/WFGY/blob/main/ProblemMap/rerankers.md)
* **Embedding mismatch** → [embedding-vs-semantic.md](https://github.com/onestardao/WFGY/blob/main/ProblemMap/embedding-vs-semantic.md)
* **Fragmentation drift** → [vectorstore-fragmentation.md](https://github.com/onestardao/WFGY/blob/main/ProblemMap/vectorstore-fragmentation.md)
* **Prompt instability** → [context-drift.md](https://github.com/onestardao/WFGY/blob/main/ProblemMap/context-drift.md)
---
### 🔗 Quick-Start Downloads (60 sec)
| Tool | Link | 3-Step Setup |
| -------------------------- | ------------------------------------------------------------------------------------------------------------------------------------------ | ---------------------------------------------------------------------------------------- |
| **WFGY 1.0 PDF** | [Engine Paper](https://github.com/onestardao/WFGY/blob/main/I_am_not_lizardman/WFGY_All_Principles_Return_to_One_v1.0_PSBigBig_Public.pdf) | 1️⃣ Download · 2️⃣ Upload to your LLM · 3️⃣ Ask “Answer using WFGY + \” |
| **TXT OS (plain-text OS)** | [TXTOS.txt](https://github.com/onestardao/WFGY/blob/main/OS/TXTOS.txt) | 1️⃣ Download · 2️⃣ Paste into any LLM chat · 3️⃣ Type “hello world” — OS boots instantly |
---
### 🧭 Explore More
| Module | Description | Link |
| ------------------------ | ---------------------------------------------------------------------------- | -------------------------------------------------------------------------------------------------- |
| WFGY Core | WFGY 2.0 engine is live: full symbolic reasoning architecture and math stack | [View →](https://github.com/onestardao/WFGY/tree/main/core/README.md) |
| Problem Map 1.0 | Initial 16-mode diagnostic and symbolic fix framework | [View →](https://github.com/onestardao/WFGY/tree/main/ProblemMap/README.md) |
| Problem Map 2.0 | RAG-focused failure tree, modular fixes, and pipelines | [View →](https://github.com/onestardao/WFGY/blob/main/ProblemMap/rag-architecture-and-recovery.md) |
| Semantic Clinic Index | Expanded failure catalog: prompt injection, memory bugs, logic drift | [View →](https://github.com/onestardao/WFGY/blob/main/ProblemMap/SemanticClinicIndex.md) |
| Semantic Blueprint | Layer-based symbolic reasoning & semantic modulations | [View →](https://github.com/onestardao/WFGY/tree/main/SemanticBlueprint/README.md) |
| Benchmark vs GPT-5 | Stress test GPT-5 with full WFGY reasoning suite | [View →](https://github.com/onestardao/WFGY/tree/main/benchmarks/benchmark-vs-gpt5/README.md) |
| 🧙♂️ Starter Village 🏡 | New here? Lost in symbols? Click here and let the wizard guide you through | [Start →](https://github.com/onestardao/WFGY/blob/main/StarterVillage/README.md) |
---
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