Minimum detectable effect (MDE)
In practice, for a UK buyer
The paragraph above is the neutral answer. This is the part a vendor glossary leaves out.
The number that tells you whether a test is worth running before you run it. If your design's MDE is a 30% lift and a realistic lift is 5%, the experiment cannot answer your question and should not be commissioned. AdBuyMCP returns the MDE alongside an underpowered verdict precisely so the answer is actionable — you learn what would have to change rather than only that it failed.
What this one connects to
Most confusion in media buying comes from two adjacent terms being used interchangeably, so these are the neighbours worth reading next.
Statistical power
The probability that a test will detect a real effect of a given size, if an effect of that size genuinely exists in the population being measured. A design with low power will usually miss a genuine effect, raises the share of the results it does produce that are noise rather than signal, and exaggerates the size of the effects it does detect.
Geo-lift test
An experiment that runs advertising in some geographic markets and withholds it from comparable others, then compares outcomes between them. The causal design that needs no login, pixel or match rate.
Incrementality
The share of an outcome that happened because of the advertising, measured against what would have happened anyway. Measured by comparing an exposed group with a comparable unexposed one, not by counting conversions that followed an advert.
More on measurement and evidence
What you can prove afterwards, and the difference between a number that means something and a number that does not.
45 minutes. Bring a real brief and we compile it live. You describe one audience and watch it compile into seven targeting specifications, each with the score for how much of the definition survived.
Talk it through