In the most fundamental sense, there are only two ways of increasing the output of the economy: (1) increase in the number of inputs that go into the productive process, or (2) think of new ways in which more output can be produced from the same number of inputs. Especially for an economist it is curious to know which of these two ways has been more important - and how much more important. Essentially what Abramovitz did was to measure the growth in the output of the American economy between 1870 and 1950. Then he measured the growth in inputs (of capital and labor) over the same time period. He then made what were thought to be reasonable assumptions about how much a growth in a unit of labor and how much a growth in a unit of capital should add to the output of the economy. It turned out that the measured growth of inputs (i.e., in capital and labor) between 1870 and 1950 could only account for about 15% of the actual growth in the output of the economy. In a statistical sen...