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The Experiment Journal

A/B testing and statistics.

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Test Design

A worked scenario for designing a trustworthy A/B test: pre-commit sample size, avoid peeking, check sample ratio mismatch, and choose the right stati...

Case Studies

Most A/B test wins are false positives. Learn why peeking, low power, and ignoring practical significance inflate your results—and how to run tests th...

Test Design

Peeking at your A/B test inflates false positives to 30%. I argue for sequential testing methods that let you monitor without ruining your results.