Difference-in-differences
In practice, for a UK buyer
The paragraph above is the neutral answer. This is the part a vendor glossary leaves out.
The readout underneath a geo-lift result. It is worth understanding because it explains what the test is actually robust to: shared shocks cancel, but anything that hit only the test markets does not. That is the residual risk in any geo experiment and the reason a result should carry a confidence interval rather than a single number.
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.
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.
Matched market
A control market chosen because its historical outcome pattern closely tracks the test market's, so that a later divergence can be attributed to the campaign.
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.
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