Why can 99 percent accuracy still mean a failed model?
PICTURE THIS: 1, 2, 2, 8
Simple meaning
If 99 percent of rows are negative, always predicting negative scores 99 percent and finds zero fraud.
WHY — Imbalanced Data instead of guessing?
Why interviewers care about Imbalanced Data:
on Imbalanced Data.
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:
- 1If 99 percent of
rows are negative, always predicting negative scores 99 percent and finds zero fraud.
- 2You must inspect rare-class
recall, precision, PR-AUC, or dollar cost.
- 3This is a standard
metric-sense interview trap.
- 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
If 99 percent of rows are negative, always predicting negative scores 99 percent and finds zero fraud. You must inspect rare-class recall, precision, PR-AUC, or dollar cost.