Replying here, because I cant reply to your comment several levels down.
I can see how you would have that perspective as a third-party analyst of conversion.
It's actually easy to do if you are the exchange/sell-side provider of the advertising space. In your logic, where the advertiser running the incrementality study would have won the auction, just randomly remove their bid from some won auctions, have the second highest bidder win, and then track that user as the "control" for conversion purposes vs. users you did display the ad to. Voilà!
That's not observation. That's statistical inference. I am referring, strictly, to direct, empiricial observation. With any kind of statistical inference, you get into a pissing match about assumptions, model quality, etc... Is the "control" a good stand-in for the behavior of the "test", etc.
Incrementality is able to be estimated, but unobservable. And therein lies the potential for fraud.
Sure, if by unobservable you mean in the same way that we can't truly "observe" the population average height of humans, even if we can probably get a pretty darn good estimate.
You can observe the results of the experiment and then make statistical inference about the "true" incrementality. You don't even have to perform inference necessarily, you can just provide the direct results of your experiment to the advertiser and let them do the inference.
But I do fail to see how a third-party could possibly infer this measure, given that they have no capacity to do a true incrementality experiment on the platform.
Are you running the incrementality study, or is your provider (e.g. Google)? Because one of the points here is that providers also have an incentive to fudge the numbers - they're not in business of being accurate, they're in business of making it seem their services help you.
To riff off the average height example - you can get a pretty darn good estimate based on sampling and good statistical practice... unless the people doing the sampling have a reason to bias the measurement, or - if you're sampling on your own - people who control where you go and who you meet...
Oh that could definitely be the case, although I'll note that the larger actors have more to lose and are at more risk of being caught for engaging in fraud.
I think my usage of "you" was confusing because I work in sell-side advertising.
You nailed this. Tirole discusses this in his paper hierarchy on bueracracies. Your internal stakeholders aren't always aligned to the company, sometimes it is to a vendor.
I can see how you would have that perspective as a third-party analyst of conversion.
It's actually easy to do if you are the exchange/sell-side provider of the advertising space. In your logic, where the advertiser running the incrementality study would have won the auction, just randomly remove their bid from some won auctions, have the second highest bidder win, and then track that user as the "control" for conversion purposes vs. users you did display the ad to. Voilà!
That's not observation. That's statistical inference. I am referring, strictly, to direct, empiricial observation. With any kind of statistical inference, you get into a pissing match about assumptions, model quality, etc... Is the "control" a good stand-in for the behavior of the "test", etc.
Incrementality is able to be estimated, but unobservable. And therein lies the potential for fraud.