DoubleClick used comScore's panel of 1.5m US internet consumers to identify people who made purchases on one of 30 sites in four categories: apparel; computer hardware; sports/fitness; and travel.
The internet media group then captured all relevant search activity of those buyers during the 12 weeks leading up to purchase.
The study 'Search before the Purchase', carried out in conjunction with DoubleClick's marketing division Performics, was developed to demonstrate how consumers use search engines in the process of making purchases online.
Key findings of the study revealed that the majority of people in pre-purchase search activity, using searches and clicks, involve generic terms such as "running shoes" as opposed to a merchant brand.
Branded terms only dominated the search activity closer to the purchase, peaking in "same session" search activity.
Stuart Larkins, vice-president of Performics, said: "Marketers should track search click-throughs for weeks prior to the purchase session to fully account for the longitudinal impact of generic keywords in search."
He added that generic keywords provided greater reach for marketers and contributed to the overall lift in a search programme.
The findings come as the 2005 Online Marketing Attitudes reveal that UK consumers are much more aware of search engine marketing techniques than Americans.
According to the study, 93% of British consumers know the difference between sponsored and organic search engine results compared with just 38% of Americans.
UK consumers are most responsive to natural search engine results and only a few regularly click on sponsored links, according to research commissioned by online marketing group Agence Virtuelle.
Stephane Perino, founder and CEO of Agence Virtuelle, said: "The increasing cost of certain keywords coupled with growing consumer awareness and scepticism of sponsored links and their preference for organic search engine results requires marketers to increase their investment in search engine optimisation and find a more appropriate balance with search engine marketing."
In the UK, it was also revealed that Google was the favourite seach engine for delivering the most relevant results.
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