Writing

Average retention across all cohorts mixes customers with different lifetimes and lies upward. How to build a triangular cohort matrix, read observation age, and compare cohorts honestly.

A p-value from a textbook doesn't prove a method — a simulation does. How to test every A/B module with an A/A check under the null and a power curve under the effect: CUPED, peeking, ratio metrics, mSPRT.