"What ‘work' does advertising do and how well does it do it? Aside from comforting purchasers by assuring them they made the right choice, aside from comforting CEOs and employees that their work is important, and aside from certain unpredictable short-term increases in consumption, most advertising does not perform as advertised. Take away the tax deductions that corporations get for advertising, and most expenditures would dry up overnight.
Although elaborate proofs of advertising’s impotence are available, the simple fact is that you cannot put a meter on the relationship between increased advertising and increased sales. If you could, (ad) agencies would charge by how much they have increased sales, not by how much media space they have purchased.
Neil H. Borden of the Harvard Business School first demonstrated the inconclusiveness of most advertising in his definitive work, The Economic Effects of Advertising (1942), and Michael Schudson reconfirmed Borden's thesis in 1984 in Advertising: The Uneasy Profession. (page 109)