Glossary · Testing · also MDE
What is the minimum detectable effect (MDE)?
The minimum detectable effect (MDE) is the smallest change a test can reliably distinguish from noise, given its traffic, baseline rate and duration. It decides whether a test is worth running at all, and it is too often calculated after a test disappoints rather than before it starts.
- Reviewed 6 October 2026
In more detail
Running the calculation first changes what you test. If your traffic can only detect a lift far larger than a button colour could plausibly produce, a button-colour test is not a test: it is a way of spending weeks to learn nothing.
The two levers are the event rate and the effect size. You cannot raise the effect size on demand, but you can move to a more frequent event: judging at add-to-cart instead of purchase can shrink the detectable effect enough to make a test viable on the same traffic.
Key points
- Decides in advance whether a test can conclude at all.
- Driven by baseline rate, traffic volume and duration.
- Moving to an earlier, more frequent judging step is the main practical lever.
How Liftable relates
Related terms
Guides that go deeper
Last reviewed against the product on 6 October 2026.
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