When is accuracy a bad metric?
PICTURE THIS: HOW TO EXPLAIN IT
Simple meaning
On imbalanced data, predicting the majority class always looks accurate but useless.
WHY — Metrics instead of guessing?
Why interviewers care about Metrics:
on Metrics.
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:
- 1On imbalanced data, predicting
the majority class always looks accurate but useless.
- 2Precision, recall, and F1
tell a fairer story.
- 3Fraud and disease screening
are classic examples.
- 4Give an example
One tiny concrete case you can say aloud.
- 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
On imbalanced data, predicting the majority class always looks accurate but useless. Precision, recall, and F1 tell a fairer story.