Patent Citation Analysis

Patent citation analysis uses the references that patents make to earlier patents as quantitative traces of innovation value and the flow of technological knowledge. The approach was given its empirical foundation by Adam Jaffe, Manuel Trajtenberg, and Rebecca Henderson, whose 1993 Quarterly Journal of Economics study used patent citations to show that knowledge spillovers are geographically localized - inventors disproportionately build on nearby prior art. Bronwyn Hall, Adam Jaffe, and Manuel Trajtenberg's 2001 NBER work then assembled the large-scale patent-citations data file and the methodological toolkit - forward-citation counts, generality and originality indices, citation lags, and self-citation measures - that made citation analysis a standard instrument in the economics and strategy of innovation. By treating the citation network as data, researchers can measure how important an invention is, where its knowledge came from, and where it flowed.