Why are BLEU and ROUGE weak metrics for open-ended LLM answers?
PICTURE THIS: AN LLM TURN
Simple meaning
They reward n-gram overlap with a reference, but many correct phrasings exist.
WHY — Evals instead of guessing?
Why interviewers care about Evals:
on Evals.
the situation, the default choice, and one exception - that reads as experience.
Name the idea, why it exists, then one short example.
End with when you use it and one common pitfall.
STEPS — What happens step by step?
Before you speak the answer, walk the interviewer through these steps:
- 1They reward n-gram overlap
with a reference, but many correct phrasings exist.
- 2Why it exists
A good paraphrase scores low
- 3a copied wrong sentence
can score high.
- 4Prefer task-specific checks, rubrics,
and human or judged scores.
- 5Common mistake
What juniors usually get wrong.
- 6Close
When you pick this over the alternative.
EXAMPLE — See it in action
Here's a short line you can speak, broken into clear beats:
Note: Adapt this scaffold to your own project — keep it under 60–90 seconds.
Key takeaway
They reward n-gram overlap with a reference, but many correct phrasings exist. A good paraphrase scores low