RAG evaluation and comparison with alternatives
Practice this questionOverview
- RAG evaluation measures retrieval quality and answer quality independently and together.
- Fine-tuning changes model behavior through training; long context supplies a large body of content directly; traditional search returns evidence without generating an answer.
- These approaches solve different parts of the problem.
Why this matters
You need to know whether missing evidence or poor generation causes errors, and whether RAG adds value over simpler alternatives.
An everyday example
Check both whether an employee opened the correct pages and whether their explanation followed those pages.
A technical example
For a labeled policy question, measure recall@10, ranking quality, supported claims, correct citations, final correctness, latency, and cost.
How it works
- Create source-grounded cases
- Label eligible relevant evidence
- Run retrieval
- Run generation
- Score independently
- Inspect failure categories
- Compare baselines.
Architecture and flow
Golden questions + source labels → retrieval metrics + answer metrics → regression gate.
The insurance assistant example
Test two policy versions, absent answers, cross-tenant queries, and questions containing misleading premises.
When to use it
Before shipping or changing parsing, indexing, chunking, models, prompts, or rerankers.
When to avoid it
Do not optimize one aggregate score while hiding severe failures in exclusions, privacy, or source freshness.
Interview answer
“I evaluate retrieval recall and ranking separately from faithfulness and answer correctness, then compare the full system against search and long-context baselines.”
Benefits, trade-offs, and production considerations
- RAG still needs an authoritative source; fine-tuning is usually for behavior, not a frequently changing knowledge database.
- A model can faithfully repeat an outdated document, so faithfulness alone is insufficient.
| Approach | What it changes/provides | Good fit | Main trade-off |
|---|---|---|---|
| RAG | Selects external knowledge at request time | Large/changing private corpus, citations | Ingestion and retrieval maintenance |
| Fine-tuning | Learns behavior/style/task patterns in weights or adapters | Repeated stable task failures with good training data | Training cost, data governance, regression risk |
| Long context | Places supplied content directly in the request | A bounded set of documents already known for this task | Repeated input cost, attention limitations, eligibility filtering still needed |
| Traditional search | Returns source results | Users can read evidence directly or accuracy demands exact excerpts | Less conversational synthesis, often lower generation risk/cost |