17. A non-transitory computer readable medium storing computer executable instructions which when executed on a computer simulate a process, the instructions comprising instructions to: identify a first change made by an advertiser to a paid portion of the search advertising campaign, the first change affecting a cost of the paid portion; determine 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; process 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 store the first synergy score in a machine readable memory in association with an indication of the first change.
17. A non-transitory computer readable medium storing computer executable instructions which when executed on a computer simulate a process, the instructions comprising instructions to: identify a first change made by an advertiser to a paid portion of the search advertising campaign, the first change affecting a cost of the paid portion; determine 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; process 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 store the first synergy score in a machine readable memory in association with an indication of the first change. 25. The computer readable medium of claim 17 , wherein the instructions further comprise instructions to: determine a value of the first change based at least in part on the first synergy score, a revenue associated with the paid portion, and a cost associated with the paid portion.