Through a survey, economic value estimates were obtained on 962 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 a count of citations to those patents. Patents renewed to full term were significantly more valuable than patents allowed to expire before their full term. The higher an invention's economic value estimate was, the more the relevant patent was subsequently cited.
Harhoff, Dietmar, F. Narin, F. M. Scherer und K. Vopel (1997), Citation Frequency and the Value of Patented Innovation, ZEW Discussion Paper No. 97-27, Mannheim. Download