For example, Michael Perelman has argued in his 1989 book "Keynes, Investment Theory and the Economic Slowdown: The Role of Replacement Investment and q-Ratios" that the US Federal Reserve Board measure is just not very revealing. Prior to the early 1980s, he argues, American business carried a great deal of extra capacity. At that time, running close to 80% would indicate that a plant was approaching capacity restraints. Since that time, however, firms scrapped much of their most inefficient capacity. As a result, a modern 77% capacity utilization now would be equivalent to a historical level of 70%.