Pioneering Inventors or Thicket Builders: Which U.S. Firms Use Continuations in Patenting?

Why do firms use continuations in the prosecution of their patents? Motivated by the widespread use of continuations by U.S. firms and the prominence of this procedure in U.S. patent policy debates, we investigate the influence of corporate and patent characteristics on the use of continuations. We employ novel data on applicants and their filings of three types of continuations--the continuation application (CAP), the continuations in part (CIP), and divisions--during 1981-2000 to distinguish among the motives for continuing patents. We find that CIPs are disproportionately filed by research and development-intensive firms that patent heavily, and that these continuations are more common in chemical and biological technologies. Patents issuing from CIPs cover relatively important inventions and their use appears consistent with a strategy of protecting "pioneering inventions." In contrast, CAPs and divisions are associated with less important patents assigned to capital-intensive firms, particularly in computer and semiconductor fields, and appear to be used in defensive patenting strategies. We analyze the effects of the 1995 change in patent term, and find that the act reduced continuations overall and shifted the output of continuations toward less important patents.