CPA
In practice, for a UK buyer
The paragraph above is the neutral answer. This is the part a vendor glossary leaves out.
The most quoted and least comparable number in media. Two CPAs are only comparable if they share an attribution window, a model and a definition of the action, and they almost never do. A CPA computed on last-click will always flatter search and starve everything that created the demand. This is the number an incrementality test exists to check.
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.
Attribution
Assigning credit for an outcome to the advertising touchpoints that preceded it, according to a rule the advertiser chose. A description of correlation in a conversion path, not a demonstration that the advertising caused anything.
Last-click attribution
An attribution rule that gives all the credit for an outcome to the final advertising touchpoint before it, and none to the rest. Simple, universally available, and systematically biased towards whichever channel sits closest to the conversion.
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.
Cost per outcome (CPO)
A pricing model in which the advertiser pays only when a defined outcome occurs — an install, a purchase, a store visit — with the platform carrying the delivery risk and embedding its margin in the outcome price.
More on buying and commercials
How media is transacted and where the money goes. The terms in this group are the ones a fee conversation turns on.
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