Through a survey, private economic value estiamtes were obtained on 964 inventions made in the United States and Germany and on which German patent renewal fees were paid to full-term expiration in 1995. A search of subsequent U.S. and German patents yielded counts of citations to those patents. Patents renewed to full-term were significantly more highly cited than patents allowed to expire before their full-term. The higher an invention's economic value estimatewas, the more the patent was subsequently cited.
Harhoff, Dietmar, Francis Narin, F.M. Scherer and Katrin Cremers (1999), Citation Frequency and the Value of Patented Inventions, The Review of Economics and Statistics 81(3), 511-515.