The hunt for S-shaped growth paths in technological innovation: a patent study*

Since the works by the business cycle theorists in the 1930s, no attempts have been made to study empirically the long term evolution paths of individual technologies starting with long time series. This is an empirical exploration and confirmation of the now almost assumed image or metaphor of the way technology develops; that it follows an S-shaped growth path which is commonly associated with a similar shaped diffusion function of entrepreneurial activity. The paper also confirms the diversity of technology dynamics and explores how technological cycle takeoffs appear to be clustered within certain historical epochs. The results have implications for our understanding of the evolution paths of individual technologies, and of the evolution of technological systems and waves of innovation. By use of computational statistics, logistic growth functions are fitted to US patent stocks, 1920–1990, at a detailed level of aggregation, including chemical, electrical/electronic, mechanical, transport and non-industrial technologies. Some practical considerations when developing an empirically testable model of innovation cycles are addressed in the paper as well.