The study was conducted by DoubleClick's search marketing division, Performics, and comScore, which examined its panel of 1.5 million U.S. Internet users to determine how they used search engines in the process of making online purchases through the month of September. "This study confirms what we've believed to be true for some time," Stuart Larkins, vice president of partner services at DoubleClick's Performics, said Monday.

The study, "Search Before the Purchase," analyzed pre-purchase search activity across four categories --apparel, computer hardware, sports and fitness, and travel--and found that nearly half of all online shoppers conducted related research at a search engine before making an online purchase.

The study also found that most searchers complete their purchase-related search activity weeks in advance of the purchase transaction. Far too many marketers, said Larkins, base the success of search marketing programs on clicks that lead to a purchase in the same session, or a few days post. But the study concluded that most buyers complete their purchase-related research two or more weeks before they hand over their credit card numbers.

In the travel category, 64.7 percent of buyers' final searches occurred at least two weeks before the purchase event, and 21.6 percent searched one week or more before purchase. Only about one in four --23.8 percent--bought during the same session.

"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," said Larkins. "Generic keywords provide greater reach for marketers and contribute to the overall lift in a search program."

Overall, the study found that approximately one out of every two online purchases was preceded by research on a search engine. The number of searches prior to purchase varied by category. For instance, apparel buyers made 4.7 relevant searches; computer hardware buyers, 4.9; and travel buyers averaged 6 relevant searches in the 12 weeks before their transaction, according to the study.

This news story is important. I recommend that everyone read it.