Big Data zeros in on ad inefficiency

John Wanamaker, the innovative Philadelphia merchant who pioneered the modern department store in the Gilded Age, was such a fan of newspapers that he is credited with buying the first full-page ad.  

But even Wanamaker knew that the most efficient form of advertising available in the 1890s wasn’t terribly efficient at all. “Half the money I spend on advertising is wasted,” he is famously