It's being called a "world first."
A study released by England's Radio Advertising Bureau (RAB) "evaluates radio advertising effectiveness in detail in terms of revenue return on investment (ROI) across a broad dataset."
Their analysis of more than 2000 media campaigns revealed that "(o)n average radio advertisers get their money back 7.7 times over, although some categories show exceptional performance, notably automotive and retailer brands, as well as impulse products.
Here's a link to the full study, downloadable presentations, video and more from the UK Radio Advertising Bureau (RAB).