http://www.nber.org/papers/w20171.pdf http://www.nber.org/papers/w20171.pdf Just one example, but there's plenty of stock in the hypothesis that online ads rea

http://www.nber.org/papers/w20171.pdf http://www.nber.org/papers/w20171.pdf Just one example, but there's plenty of stock in the hypothesis that online ads really don't do anything to begin with.