http://systematicdirectmarketing com/marketing-strategy/direct-marketing/do-you-know-the-common-direct-marketing-measurements/

John Wanamaker, a 19th century entrepreneur, once famously made the statement, ‘I know that half of my advertising is wasted, I just don?t know which half.’ Fortunately for today’s marketers, there are scientific ways to determine which half is wasted, and which half is not, through the use of common direct marketing measurements….