In July 2011, Google released a study called "Incremental Clicks Impact of Search Advertising" that showed the amount of search ad traffic that is incremental to traffic from an advertiser’s organic search results. In that study, we asked these questions: What happens when search ads are paused? How much does organic traffic make up for the loss in traffic from search ads?
We found that an average 89% of paid clicks are essentially lost and not recovered by an increase in organic clicks when a search campaign is paused. This number - what we call the Incremental Ad Clicks (IAC) - was consistent across all verticals.
In that initial study, we only examined cases where ads were completely paused. In this update, we looked at three additional change scenarios and included new cases up to August 2011, giving a total of more than 5,300 cases.
http://googleresearch.blogspot.com/2012 ... pdate.html