Emily Steel and April Dembosky
Financial Times 
Sept 24, 2012
Facebook is working with a controversial data company called Datalogix that can track whether people who see ads on the social networking site end up buying those products in stores.
Amid growing pressure for the social networking site to prove the value of its advertising , Facebook is gradually wading into new techniques for tracking and using data about users that raise concerns among privacy advocates .
“We kept hearing back [from marketers] that we needed to push further and help them do a better job,” said Brad Smallwood, Facebook’s head of measurement and insights.
Datalogix has purchasing data from about 70m American households largely drawn from loyalty cards and programmes at more than 1,000 retailers, including grocers and drug stores. By matching email addresses or other identifying information associated with those cards against emails or information used to establish Facebook accounts, Datalogix can track whether people bought a product in a store after seeing an ad on Facebook.