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Question: How many subjects are needed for an A/B test?

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Baseline conversion rate: %
10.2%
Minimum Detectable Effect: %
10.2% – 13.2%
The MDE is the smallest difference that can be detected with the prescribed number of subjects.
Conversion rates in the gray area will not be distinguishable from the baseline.
Answer:
2,545
per branch
Statistical power 1−β:
Percent of the time the minimum effect size will be detected, assuming it exists
Significance level α:
Percent of the time a difference will be detected, assuming one does NOT exist
If you like this, check out Wizard — the easy Mac statistics app.

See also: How Not To Run an A/B Test