In July 2011, Google released a study called Incremental Clicks Impact of Search Advertising, which analyzed the amount of paid ad search traffic that is incremental to traffic from organic search results, according to Google's blog. Researchers found that on average, 89 percent of paid clicks are lost and not recovered by an increase in organic clicks when a search campaign is paused.
That study was recently updated to include three more scenarios - when ad spend in decreased but not to zero, when ad spend is increased from a zero base and ad spend is increased from a non-zero base.
The authors found that in the new study, the average incremental clicks lost when an entire campaign was paused dropped slightly, to 85 percent, although some of the difference was simply attributed to seasonal factors, Search Engine Land explains.
For the other three scenarios, when ad spend was decreased but not paused, 80 percent of the traffic would not be made up by organic listings. There was also a 79 percent increase in incremental clicks when spending started up from a dead stop, and a 78 percent lift from a non-zero base.
The bottom line? Ads drive a large proportion of incremental traffic that is not replaced by navigation from organic listings.