Geo-lift test
In practice, for a UK buyer
The paragraph above is the neutral answer. This is the part a vendor glossary leaves out.
The most practical causal method available to a brand advertiser, and the one that suits out-of-home, cinema and television — channels where person-level measurement is impossible. It needs enough independent markets, enough spend and enough conversion volume, which is why a twenty-catchment retailer can usually power one and a single national campaign usually cannot. AdBuyMCP also refuses a contaminated design: if every candidate control market received delivery from the campaign, none is a holdout, and it says so and stops.
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.
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.
Holdout
A group deliberately excluded from seeing a campaign and kept as a comparison against the group that was exposed to it. Without one, the counterfactual — what would have happened anyway — has to be assumed rather than observed.
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.
Difference-in-differences
A method that compares the change in an exposed group against the change in a control group over the same period, so that anything moving both in step — seasonality, a competitor, the weather — cancels out.
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