At this moment the penetration of broadcasts was a matter of guesswork, and relative standing of competitors in radio was a matter of little solid evidence. In the absence of even remotely scientific metrics, listeners were sometimes canvassed by phone during the evening hours or asked on air to mail in a postcard to receive some small gift—all this to get some idea of how many had heard the commercials. The success of shows like Amos ’n’ Andy and its effect on the sales of Pepsodent toothpaste made some difference, of course. It was something else, however, to prove that these were no fluke but something worth paying for.

Tim Wu, The Attention Merchants, loc. 363