Is all that spending delivering incremental conversions? The answer is most definitely “no.”
You might have gotten some of the same conversions from YouTube as from Google Search. You might have gotten all of the same conversions from Search that you got from Display. And so on and so forth.
Due to the complexity of measuring cross-stack behavior, most ad stacks don’t offer a way to measure cross-stack incrementality.
Running clean, matched-market tests, in which you compare the behavior of users in a single control region with the behavior of users in a single test region, is a good way to measure cross-stack incrementality. Another route, if you spend a whole lot on any ad stack, is to use advanced modeling like conversion modeling.
Cross-stack incrementality helps you optimize on-stack budget allocations as well as on-stack optimizations.
3. Marketing-portfolio incrementality
Measuring across all activity is the hardest part of marketing analytics.
An incrementality-curious executive might ask you: “What is the incrementality across all the marketing activity I spent money on?”
I call it marketing-portfolio incrementality.
In other words, what is the true incrementality of the money spent on Google, YouTube, Display, Facebook, cinema, print, television, channel marketing, and promotions?
How many sales did all that money really deliver? You can ask the same question for a brand metric, say unaided awareness or consideration. How much of the brand lift in metric X would not have occurred without the ad spend?
When measured correctly, the impact of incrementality on your marketing decisions can be transformative. But measuring it is really, really hard. And it can produce seemingly conflicting findings. One year, those billboards we buy in every city can be entirely useless in an incrementality context. Another year, billboards deliver so much incremental brand lift, we should shut down social-media ads. You get the idea.
Marketing-portfolio incrementality, like cross-stack incrementality, can be measured with matched-market tests.