Module
Module 4 of 5Lesson 2 of 3~20 min

Analysis pitfalls: peeking, multiple comparisons, novelty, SRM, Simpson

A well-designed test can still lead to a false conclusion if its analysis falls into one of the classic traps. The lesson teaches you to spot them in a result or a write-up, check how units were split between groups and pick the right remedy. You avoid shipping a variant that only won by chance.

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Lesson objective

By the end of this lesson, you will be able to spot peeking, multiple comparisons, a novelty effect, a sample ratio mismatch or a Simpson's paradox in a test or its report, to check a mismatch by calculation, and to choose the right countermeasure.

Topics covered

  • peeking
  • multiple comparisons
  • novelty effect
  • sample ratio mismatch
  • Simpson's paradox

Where it fits

Analyze the result

How do I read a test result without over-interpreting it or missing a problem?

Lessons in this module

  1. Read a p-value and a confidence interval
  2. Analysis pitfalls: peeking, multiple comparisons, novelty, SRM, Simpson (this lesson)
  3. Bayesian or frequentist, and which tool to choose

What you will learn in the course

This lesson is part of the course Design and analyze an A/B test

  • Decide whether an A/B test is the right method (volume, B2B, reversibility, time, ethics) and choose a suitable alternative otherwise.
  • Write a testable hypothesis, choose a sensitive, attributable primary metric, guardrails and the exposure event to log.
  • Choose the randomization unit and prevent interference between groups, including in B2B.
  • Compute a sample size and a duration from the baseline rate, the minimum detectable effect, the significance level and the power.
  • Analyze a result (p-value, confidence interval, practical significance, guardrails) and read a tool's Bayesian or frequentist output.
  • Detect and avoid analysis pitfalls (peeking, multiple comparisons, novelty effect, sample ratio mismatch, Simpson's paradox).
  • Decide based on rules written before the test and document the experiment in a reusable memo.

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