ROI-obsessed marketers historically kvetch about the lack of controls in their Google AdSense campaigns. In the early days of the ad network, they hated that they couldn't specify different prices for their ads. More recently, advertisers were granted pricing controls, but they still weren't permitted to know on which Web pages their ads appeared.

Starting this month they can. In a phased rollout beginning today, all AdWords users in the U.S. and overseas will be offered customized reports telling them exactly where their network ads have displayed and giving them site performance metrics by domain, URL, impression, click, conversion and cost.

Called a Placement Performance report, the new measurement offering promises to let AdWords customers identify which sites perform best according to their campaign objectives and which don't pass muster. They can then use Google's site exclusion tools to eliminate poorly performing sites from their buys.

Brian Axe, director of product management for AdSense, called the report good for publishers, advertisers and users alike. And he said Google's machine-learning systems will be able to improve overall relevance across AdSense by observing how marketers use the reports.

"We're not doing transparency just for transparency's sake," he said. "Our algorithms have benefited from the human input on the search side. On the content side, we haven't had the same benefit."

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