Topics and geographical diffusion of knowledge in top economic journals

We study the evolution of topics in economics and their geographical specialization by analyzing 13,233 papers from seven top journals between 1985 and 2012 and their forward citations. The share of U.S. publications declines from 75% to 64% with a corresponding increase of the European share from 12% to 24%. We use topic modeling and document the evolution of the discipline over 27 years. We estimate, with a quasi-structural model, the citation lag distribution for 18 different topics and three large geographical areas. The modal citation lag is about 6.7 years in the entire sample and 4.8 years for citations from the top 100 journals. We quantify (1) the home bias effect in citations, (2) how it fades away over time, (3) the long lasting impact of U.S. publications vis-à-vis other geographical areas, and (4) the higher speed of diffusion and faster obsolescence in the United States. (JEL A14, I23, O33, A11).