The online ad tech industry has created an extraordinarily invasive surveillance infrastructure that threatens our democracy. But the most tragic thing is how little has been gained—how poorly ad tech works despite all the data.
Even if rampant ad fraud is curbed, there's a deeper reason why ad tech doesn't work: measuring the returns to advertising is a statistical problem that's near impossible even with perfect tracking. This neat paper shows why and deserves to be better known justinmrao.com/lewis_rao_near… 
One reason why print/TV ads work—by conspicuously spending money, the firm signals to consumers that it is big & will stick around, is invested in its reputation, and has products worth advertising. Online ads don't achieve this. The more targeted the ad, the *weaker* the signal.
