A combination of paid and organic search impressions leads to the greatest uplift in purchase intent

"Amongst its key findings, the study reveals that exposure to impressions of digital media boosts brand favorability. Specifically, paid search has the greatest impact on this metric, both in isolation and in combination with other digital media types. Alone, paid search impressions create the greatest lift (28%) overall. However, when combined with organic search impressions, the organic-paid search duo boosts this metric to 40 percent. Likewise, exposure to paid search impressions nets the greatest lift (35%) of individual assets for this metric in the retail vertical. Yet the paid and organic search combination creates a lift of 56 percent for the hotel sector.
The study also reveals that exposure to impressions of digital media drives Internet users' likelihood to purchase. Paid search impressions are particularly adept at influencing this behavior, whether they are used alone or in conjunction with other digital media. At the aggregate level, paid search generates a lift of 44 percent on its own; but within the retail vertical, it produces a 54 percent lift. However, combinations of two digital media types also play a role. Together, organic and paid search impressions yield the greatest lift (73%) in aggregate and in the hotel vertical (147%). But organic and display impressions create the most effective combination (64%) for this metric in the banking/financial services sector."
Source:  Research from iProspect and comScore reported in a press release from iProspect, 2nd November 2010