NATIONAL BUREAU OF ECONOMIC RESEARCH
NATIONAL BUREAU OF ECONOMIC RESEARCH

A Theory of Growth and Volatility at the Aggregate and Firm Level

Diego Comin, Sunil Mulani

NBER Working Paper No. 11503
Issued in August 2005
NBER Program(s):   EFG

This paper presents an endogenous growth model that explains the evolution of the first and second moments of productivity growth at the aggregate and firm level during the post-war period. Growth is driven by the development of both (i) idiosyncratic R&D innovations and (ii) general innovations that can be freely adopted by many firms. Firm-level volatility is affected primarily by the Schumpeterian dynamics associated with the development of R&D innovations. On the other hand, the variance of aggregate productivity growth is determined mainly by the arrival rate of general innovations. Ceteris paribus, the share of resources spent on development of general innovations increases with the stability of the market share of the industry leader. As market shares become less persistent, the model predicts an endogenous shift in the allocation of resources from the development of general innovations to the development of R&D innovations. This results in an increase in R&D, an increase in firm-level volatility, and a decline in aggregate volatility. The effect on productivity growth is ambiguous. On the empirical side, this paper documents an upward trend in the instability of market shares. It shows that firm volatility is positively associated with R&D spending, and that R&D is negatively associated with the correlation of growth between sectors which leads to a decline in aggregate volatility.

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This paper was revised on November 10, 2006

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Published:

  • Comin, Diego and Sunil Mulani. "Diverging Trends In Aggregate And Firm Volatility," Review of Economics and Statistics, 2006, v88(2,May), 374-383. Also: Diego Comin & Sunil Mulani. "A theory of growth and volatility at the aggregate and firm level," Proceedings, Federal Reserve Bank of San Francisco, issue Nov 2007. ,
  • Comin, Diego & Mulani, Sunil, 2009. "A theory of growth and volatility at the aggregate and firm level," Journal of Monetary Economics, Elsevier, vol. 56(8), pages 1023-1042, November.

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