They Don't Invent Them Like They Used To: An Examination of Energy Patent Citations Over Time

David Popp

NBER Working Paper No. 11415
Issued in June 2005
NBER Program(s):Productivity, Innovation, and Entrepreneurship, Environment and Energy Economics

This paper uses patent citation data to study flows of knowledge across time and across institutions in the field of energy research. Popp (2002) finds the level of energy-saving 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 paper explores the pattern of citations in these fields more carefully. I find evidence for diminishing returns to research inputs, both across time and within a given year. To check whether government R&D can help alleviate potential diminishing returns, I pay special attention to citations to government patents. Government patents filed in or after 1981 are more likely to be cited. More importantly, descendants of these government patents are 30 percent more likely to be cited by subsequent patents. Earlier government research was more applied in nature and is not cited more frequently.

download in pdf format
   (370 K)

email paper

Machine-readable bibliographic record - MARC, RIS, BibTeX

Document Object Identifier (DOI): 10.3386/w11415

Published: Popp, David. "They Don't Invent Them Like They Used To: An Examination of Energy Patent Citations Over Time.” Economics of Innovation and New Technology 15, 8 (November 2006): 753-776.

Users who downloaded this paper also downloaded* these:
Popp and Newell w15423 Where Does Energy R&D Come From? Examining Crowding Out from Environmentally-Friendly R&D
Hall, Jaffe, and Trajtenberg w8498 The NBER Patent Citation Data File: Lessons, Insights and Methodological Tools
Popp w8284 Induced Innovation and Energy Prices
Popp w9978 Lessons from Patents: Using Patents To Measure Technological Change in Environmental Models
Johnstone, Hascic, and Popp w13760 Renewable Energy Policies And Technological Innovation: Evidence Based On Patent Counts
NBER Videos

National Bureau of Economic Research, 1050 Massachusetts Ave., Cambridge, MA 02138; 617-868-3900; email:

Contact Us