Innovation in the U.S. 1920-2006 - Quality Trends and Evolutionary Path

Аннотация

Long run economic growth potential depends on the increase in the efficiency of resource utilization in the economy through improvements in the underlying technological capabilities. Recent economic growth slow-down, and in particularly the substantial decline in long-run productivity growth rates in the US, raises a question regarding the possible slowdown in the underlying technological growth. I set out to evaluate this question by examining the change in the potential social benefits from technology over the period of 1944-2000 in the US. I use knowledge spillovers generated by cohorts of patented innovations as proxy to the social benefits generated by those cohorts. These can be estimated using the distribution parameters for the number of citations received by patents in a cohort. The data for the work is a newly constructed patent citations database of all US patent data from 1920-2006 with full citations from 1947 on. The first chapter introduces the new data and provides an in-depth analysis of the time-trend of its various statistical characteristics. The exposed non-stationary distribution parameter for the citation data impedes its use in the time-series analysis for extracting the innovative quality trend. A de-trending treatment to correct for this non-stationary behavior is proposed and applied. The second chapter pursues the innovative quality analysis over the period. My attempts to use the Jaffe-Trajtenberg model for knowledge spillovers with the expanded data period strained some of the model’s underlying assumptions to a breaking point.