Looking at the economy of the U nited States from 1948 to 1985, he concluded that infrastructure investments led to productivity increases, finding that a 10 percent rise in infrastructure stock over time was associated with a 4 per cent increase in productivity. The study even showed that the converse also held: declining infrastructure investment from 1970 to 1985 was responsible for declining output per capita over the same period in the United States. These findings triggered a spurt of empirical research examining the contribution of infrastructure to growth.