( Financial Times ) -- 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 . The emails and other identifying information are made anonymous and collected into groups of people who saw an ad and people who did not . Datalogix compiles a report for Facebook and its advertisers to measure which creative approaches and demographic targeting persuade people to buy specific products offline . Facebook said it is paying Datalogix for the data-matching . So far , the two companies have measured 45 campaigns and in 70 per cent of cases , for every dollar a marketer spent on Facebook it earned an additional $ 3 in incremental sales , Mr Smallwood said . Marketers are eager for more data to see how their Facebook ad campaigns perform , but some said they still are figuring out how to evaluate the new data . Ford said the information was promising , but a spokesman added that it was too early to give a formal opinion . '' Some privacy advocates question whether the practice violates the $ 9.5m settlement Facebook struck with the US Federal Trade Commission over charges that it deceived consumers by not keeping privacy promises . Facebook users are automatically included in the advertising studies conducted with Datalogix , and can not directly opt out through their Facebook account . Instead , they must go to the Datalogix website , for which Facebook has a link posted in its help centre . Jeff Chester , executive director of the Center for Digital Democracy , a privacy group , said this practice does not provide Facebook users with sufficient control over their data or with transparency over how it is being used . `` We do n't believe any of this online-offline data should be used without express consumer approval and an opt-in , '' he said . Facebook and Datalogix said individual-level purchasing data were not shared with Facebook or its advertisers . Individual Facebook user data are not shared with advertisers . Facebook said it was working with an outside auditor to monitor its practices . © The Financial Times Limited 2012 .
Facebook working with data company that tracks whether its users purchase advertised products . Comment: Privacy advocates raising concerns .