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In my opinion, if there is a measurable result it's probably going to come from the human factor as opposed to the technical/algorithmic. By human factor I mean actual organic patterns of behavior linked to see a result in both the paid and organic positions. I believe that people will 'trust' these more if they appear in both places, as they seem to be signals that are reinforcing each other. The organic result implies that this site is relevant and worthwhile. The paid result implies (rightly or wrongly) that this site is established and willing and able to pay for their position in the marketplace. The combination of these two factors, plus just the extra eyeball real estate of appearing twice on the same page, likely means you'll get more traffic. Keep in mind that this is just an opinion, and I haven't reviewed the article Simon Cullum helpfully linkedabove. The technical/algorithmic aspect I mention above is more ambiguous; essentially 'does Google give sites that pay for CPC greater consideration in organic rankings?'. As has been mentioned nobody knows, and if they did that is a giant lawsuit/loss of trust waiting to happen. Because of this actual measurable factors that would indicate Google is doing this are going to be very very thin on the ground.