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THEY DON'T INVENT THEM LIKE THEY USED TO: AN EXAMINATION OF ENERGY PATENT CITATIONS OVER TIME

This article uses patent citation data to study flows of knowledge across time and across institutions in the field of energy research. Popp [2002, Induced Innovation and Energy Prices. American Economic Review, 92(1), 160–180.] finds that the level of energy-saving research and development (R&D) depends not only on energy prices, but also on the quality of the accumulated knowledge available to inventors. Patent citations are used to represent this quality. This article explores the pattern of citations in these fields more carefully. Evidence for diminishing returns to research inputs, both across time and within a given year is found. To check whether government R&D can help alleviate potential diminishing returns, special attention is paid to citations to government patents. The government patents filed in or after 1981 are more likely to be cited. More importantly, descendants of these government patents are 30% more likely to be cited by subsequent patents. Earlier government research was more applied in nature and is not cited more frequently.