{
  "lesson": "68-rag-eval-precision-recall",
  "title": "RAG Evaluation: Precision, Recall, MRR, nDCG, Faithfulness, Answer Relevance",
  "questions": [
    {
      "stage": "pre",
      "question": "Why is recall@k usually the headline retrieval metric in production RAG?",
      "options": [
        "Recall ignores ranking",
        "Recall is required by the OpenAPI spec",
        "Recall is the same as precision in RAG",
        "Generation can drop irrelevant chunks but cannot invent an answer from a chunk it never saw, so missing the right chunk is the more expensive failure"
      ],
      "correct": 3,
      "explanation": "A retriever that misses the right chunk cannot be repaired downstream; surplus chunks waste tokens but rarely poison the answer."
    },
    {
      "stage": "pre",
      "question": "What does MRR compute?",
      "options": [
        "Token count of the answer",
        "The geometric mean of cosine similarity",
        "Median rank of the second relevant document",
        "The mean of 1 / position-of-first-relevant-document across queries"
      ],
      "correct": 3,
      "explanation": "MRR is dominated by the top of the list: rank 1 contributes 1.0, rank 2 contributes 0.5, rank 10 contributes 0.1."
    },
    {
      "stage": "check",
      "question": "When should you reach for nDCG instead of recall@k?",
      "options": [
        "When the retriever does not return scores",
        "When the corpus is small",
        "Never",
        "When the gold labels carry graded relevance (e.g. doc A is 3, doc B is 2, doc C is 1) and binary metrics lose information"
      ],
      "correct": 3,
      "explanation": "nDCG uses graded gains and a position discount; recall flattens everything to binary."
    },
    {
      "stage": "check",
      "question": "What is the difference between faithfulness and answer relevance?",
      "options": [
        "Faithfulness is a retrieval metric and relevance is a chunker metric",
        "They are the same metric with two names",
        "Faithfulness measures precision; relevance measures recall",
        "Faithfulness asks 'is the answer grounded in the retrieved context'; answer relevance asks 'does the answer address the question'"
      ],
      "correct": 3,
      "explanation": "A faithful but off-topic answer scores high on faithfulness, low on relevance; a relevant but ungrounded answer scores high on relevance, low on faithfulness."
    },
    {
      "stage": "check",
      "question": "A pipeline shows decent recall@5 but low MRR. Which stage should you investigate first?",
      "options": [
        "The generator",
        "The chunker",
        "The corpus ingestor",
        "The reranker, because the right chunk is in the top-k but not at the top"
      ],
      "correct": 3,
      "explanation": "Recall@5 means the gold is in top-5; low MRR means it is not at the top of the list. That is the rerank stage's job."
    },
    {
      "stage": "post",
      "question": "What production hazard makes a frozen qrels file dangerous over time?",
      "options": [
        "The eval suite uses up disk space",
        "Embedding vectors expire",
        "The retriever stops working after six months",
        "Qrels rot: the corpus changes and a doc that was the gold answer last quarter is no longer the right answer; metrics get reported against stale labels"
      ],
      "correct": 3,
      "explanation": "Schedule a quarterly qrels review or your metrics will be measuring the wrong thing as the corpus evolves."
    }
  ]
}