The study, titled "From Clicks to Bricks: The Impact of Online Pre-Shopping on Consumer Shopping Behavior," compared the purchasing behavior of more than 175,000 comScore panelists over a period of eight months--an unexposed control group and a group that had been exposed to ads from five major retailers, including JC Penney.

Retailers saw an 83% lift in dollars spent per in-store purchase from consumers who saw both display and search ads, compared to 26% and 11% lifts from search or display ads, respectively.

They saw a 90% lift in incremental in-store revenue overall from the combination, in contrast to the 43% and 15% increases from search or display.

During the course of the study, Yahoo says that the campaigns generated more than $10 billion in total revenue for their advertising partners--nearly a quarter of which was incremental.

The study also found that a joint display and search campaign was more effective at converting online researchers to in-store purchasers--as the combination pushed 43% more in-store purchases than search (26%), or display (6%) alone.

Display's effectiveness at driving in-store activity lagged far behind search in all categories, but when it came to increasing online user engagement, the two methods had similar lift rates, with display ads increasing the number of page views by 37% compared to search's 46%.

The combination of the two still trumped both ad types on their own--causing a 68% increase in pages viewed on the retailer's own Web sites.

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