An issue that remains for further study is the extent to which the results may be tainted by systematic biases in the patent approval process that generates citations. Our maintained hypothesis is that the citation process itself does not differ depending on the domicile of the inventor. One possible bias is introduced by the fact that we are examining citations within the U.S. patent system. If a given invention is covered by patents issued in more than one country, then the obligation to cite this invention can be discharged by a citation to any of the members of the patent “family” around the world that cover the same invention in different countries. Further, U.S. inventions are often patented in the U.S. but not in Japan, while Japanese inventions patented in the U.S. are usually also patented in Japan.

As a result, localization of citations to U.S. patents might be explained by a tendency of Japanese inventors to cite the Japanese patent covering prior art rather than the U.S. patent on the same invention, combined with the fact that such a patent will often be unavailable for U.S.-invented patents. This would not, however, explain why U.S. patents issued to Japanese inventors are more likely to cite other U.S. patents issued to Japanese inventors than they are to cite U.S. patents issued to German inventors; if anything, the bias introduced by patent families would suggest that our estimates of localization for citations to countries other than the U.S. are understated.

Our basic goal in this paper was to explore the process by which citations to a given patent arrive over time, how this process is affected by characteristics of the cited patent, and how different potentially citing locations differ in the speed and extent to which they “pick up” existing knowledge, as evidenced by their acknowledgment of such existing knowledge through citation. payday loans direct lenders only

Recognizing that many inventions are never patented, that knowledge can flow from one inventor to another without being acknowledged by a citation, and that many citations probably do not reflect knowledge flow, we nonetheless view this process as a useful window into the otherwise “black box” of the spread of scientific and technical knowledge. The value of this view could obviously be enhanced, however, by a deeper understanding of the relationship between patent citations and knowledge flows. This will require more qualitative and institutional examination of inventions, patents and citations. A fruitful avenue is to build on the work of Jaffe, Fogarty and Banks by using inventors’ detailed knowledge of the technological relationship between inventions to “test” the links implied by citations.