Called Campaign Insights, the tool compares a pool of thousands of Internet users who saw an ad with an equal-size group of users who did not, then measures any difference in searches and Web site visits directly attributable to the ad. This approach differs from most display ad assessment tools that typically compare Web site visits or click-through trends following a display ad campaign.

Google has said it wants to improve its display ad programs for marketers, in a direct challenge to market leader Yahoo. The company continues to add new partners and advertisers to its YouTube video site, and in September debuted DoubleClick Ad Exchange, allowing publishers to list their unsold ad space for purchase by ad networks and other publishers.