Advertisers have many tools to measure "ghost ads" aka "people who haven't seen an ad but would otherwise have qualified for all your target criteria". See https://papers.ssrn.com/sol3/papers.cfm?abstract_id=2620078 as an example.

That's of course possible to measure in theory. I meant it as a response to "Facebook, Google and others make these tests possible in their platforms" since I haven't seen it exposed as an explicit option on either.

Then you haven't been talking to the right ad sales teams. Google and Facebook have entire product options built around this specific concept. You can run a "ghost ads" test on Google for as little as $20k in ad spend; it's relatively accessible even for smaller players.

For Facebook, Reach ads have a brand lift objective that will estimate for you. If you spend large amounts they have a measurement team that will run the actual study for you. Source: I'm running one right now for a CPG brand.

You can run this yourself without any help from them: show one group ads for your site, and show another group white rectangles. Compare performance.

Facebook has this exactly this tool, aka Conversion / Brand Lift [1]. It's a real experimentation system, not a "simulated" one like Google's Ghost Ad.

[1] https://www.facebook.com/business/help/688346554927374

Yep. Lift tests are solid gold. A lot of people pan FB ads but the reality is they can be very incremental.

The flip side is that not every campaign, targeting strategy or ad will be incremental. You have to test and retest your way to it. A blanket assumption won’t work.

Off the top of my head, you could do geographic bucketing. Take say 100 cities, and only run ads in 50 of them.

Geo tests are useful for sure, but also require a lot of data to get statistically significant results. Any noise in your data (seasonality, PR, etc) has to be taken into account as well. They’re harder to execute in general but can work well.

The interest is more on markets than individuals, in general, so what you're measuring is market response given advertising exposure, or more critically, ROI given spend.

The fact that Web and AdTech allow the appearance of individual-level targeting does not necessarily make that a Good Thing.