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Glossary
Minimum Detectable Effect (MDE)
The smallest improvement in conversion rate that you want your A/B test to be able to detect.
What is Minimum Detectable Effect?
Minimum Detectable Effect (MDE) is a threshold you set before starting a test. It defines the "magnitude" of change you care about.
For example, if your current conversion rate is 5%, you might set an MDE of 10% (relative). This means you want to be able to detect if Variant B increases the conversion rate to 5.5% or higher.
Why MDE Matters
MDE has a massive impact on your required **sample size**.
- Smaller MDE: Requires more traffic to detect (harder to see small changes).
- Larger MDE: Requires less traffic (easier to see big changes).
Choosing Your MDE
Think about the "cost" of making the change. If switching to Variant B is expensive or risky, you'll want a larger MDE to ensure the improvement is worth it.