Facts about Banner and Display Advertising
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I disagree with those who assume it's all useless because they've never personally clicked on any ads ("After all it’s a $16 Billion market. Nobody would spend that much money, without any realistic returns"), but the trends are also pretty clear. Sometimes I feel like retargeting is the last great scheme to squeeze more conversion out of the whole model. But there will probably be at least a couple more...
[0]http://econsultancy.com/us/blog/10487-view-through-attributi...
The key is to measure the effect that your display ads are having on your paid search ads, ie measure the "brand effect" impact on purchase decisions.
The direct effect of banners ads is negligible, but that is missing the point. Nobody clicks on a Coca-Cola TV ad, but they aren't going to stop TV ads anytime soon.
Our startup is also currently building a product which will help publishers improve ad performance by using continuous testing, machine learning and optimization.