Advertising's Century of Flat-Line Growth

Looking at data since the 1920s, the U.S. advertising industry has always been about 1 percent of U.S. GDP.

“Advertisers have failed to convince the client community of the value of advertising as an investment.” The ratio of sales to ad spending has remained stubbornly flat at 3.5 percent for a century.

http://www.bloomberg.com/bw/articles/2014-03-03/advertisings-century-of-flat-line-growth