1. A computer implemented method for determining an impact of a change to a paid portion of a search advertising campaign that is associated with a website, comprising: identifying a first change made by an advertiser to the paid portion of the search advertising campaign, the first change affecting a cost of the paid portion; determining, with a first computing device, one or more effects of the first change, the one or more effects being indicative of: a change in a volume of search traffic resulting from the paid portion, and a change in a volume of search traffic resulting from an unpaid portion of the search advertising campaign; processing, with the first computing device or a second computing device, the one or more determined effects to generate a first synergy score, wherein the first synergy score quantifies an impact of the first change on the volume of search traffic resulting from the unpaid portion; and storing the first synergy score in a machine readable memory in association with an indication of the first change.