Machine Learning System Design Interview, issue 11, Nov 29, 2025
The ROC Curve Mirage
Machine Learning Engineer interview at Google, and the interviewer asks:
“Is this model ready to ship?”
Why a “perfect” 0.98 ROC AUC can be worthless in fraud detection - and how PR AUC exposes the truth.
The full answer, with the mechanism and the arithmetic, is for paid subscribers on Substack.