@techreport{NBERw3903,
 title = "Productivity and Machinery Investment: A Long Run Look 1870-1980",
 author = "J. Bradford De Long",
 institution = "National Bureau of Economic Research",
 type = "Working Paper",
 series = "Working Paper Series",
 number = "3903",
 year = "1991",
 month = "November",
 URL = "http://www.nber.org/papers/w3903",
 abstract = {Over the past century the long-run growth of six economies shows a strong association between investment in machinery and economic growth that holds both within and across nations and periods. A similar strong association holds for the post-world War II period for a broader cross section of nations. A number of considerations suggest that this association is causal, and that a high rate of machinery investment is a necessary prerequisite for rapid long-run productivity growth - a hypothesis also supported by narratives from the history of technology.},
}