In this research, the authors examined how the number of organic clicks changed
when search ads were present and when search ad campaigns were turned off. The
authors developed a statistical model to estimate the fraction of total clicks that
could be attributed to search advertising. A meta-analysis of several hundred of
these studies revealed that more than 89 percent of the ads clicks were
incremental, in the sense that those visits to the advertiser's site would not have
occurred without the ad campaigns.