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All lessons in Digital and Web Analytics Lesson 5.5 of 32

Introduction to A/B testing

Your roadmap for this lesson

  • How an A/B test works
  • The six steps of a sound test
  • Mistakes that ruin test results

Short answer

An A/B test shows two versions of a page to similar users at the same time and measures which converts better. Start with a hypothesis, change one main element, split traffic randomly, and run until you reach enough sample size and statistical significance. Then roll out the winner and record what you learned.

Six steps

  1. Form a hypothesis: “Showing shipping cost on the product page will raise add-to-cart rate because users fear hidden fees.”
  2. Create versions: A (control) and B (variant), changing one main element.
  3. Split traffic randomly.
  4. Run long enough: enough sample size and at least one full business cycle (usually 2 or more weeks).
  5. Check significance: commonly 95% before declaring a winner.
  6. Implement and document the winner and what you learned.

Common mistakes

  • Stopping early because one version looks ahead after two days.
  • Testing too many changes at once, so you cannot tell what worked.
  • Ignoring segments: a winner on desktop may lose on mobile.

Quick quiz

1. Why not stop a test after two days?
2. What is the control?

Your action

Key terms

A/B test
A comparison of two versions with split traffic.
Control
The original version, A.
Variant
The changed version, B.
Statistical significance
Confidence that a result is not due to chance.

Questions beginners ask

How long should a test run?

At least one full business cycle, usually two weeks or more.

What if my site has little traffic?

Test bigger changes, or use surveys and recordings instead.

Related lessons

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