International Knowledge Flows: Evidence From Patent Citations

This paper explores the patterns of citations among patents taken out by inventors in the U.S., the U.K., Francc. Germany and Japan. We find (I) patents assigned to the same firm are more likely to cite each other, and come sooncr than other citations; (2) patents in the same patent class are approxinlatcly 100 titlles as likely to cite each other as ydtents froin different patent classes, but there is not a strong time pattern to this effect; (3) patents whose inventors reside in the same country are typically 30 to 80% more likely to cite each other than inventors from othcr countrics, and these citations come sooner; and (4) there are clear country-specific citation tendencies, e.g., Japanese citations typically come sooner than those of othcr countries.