There was a freakanomics podcast 2-part episode on advertising which discussed this, and many other things. At least in one case (eBay?) they discovered this k

There was a freakanomics podcast 2-part episode on advertising which discussed this, and many other things. At least in one case (eBay?) they discovered this kind of brand advertising had essentially zero effect. Turns out if people search for eBay, they are going to click the result for eBay, whether it is first or not.