Articles on product analytics, A/B testing, and data science by Nikita Boyarkin.https://nikitaboyarkin.github.io/en/en-usThu, 01 Oct 2026 20:58:05 GMThttps://nikitaboyarkin.github.io/en/posts/cohort-triangles-retention/https://nikitaboyarkin.github.io/en/posts/cohort-triangles-retention/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.Mon, 10 Aug 2026 00:00:00 GMTguideretentioncohort-analysispythonpandashttps://nikitaboyarkin.github.io/en/posts/ab-calibration-simulation/https://nikitaboyarkin.github.io/en/posts/ab-calibration-simulation/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.Wed, 05 Aug 2026 00:00:00 GMTguideab-testingstatisticspython