The prevalence of weak patents in the United States: A new method to identify weak patents and the implications for patent policy

The presence of patents with dubious validity (i.e., weak patents) has been one of the prominent patent policy issues with undesirable consequences in innovation. The present study empirically examines the prevalence of weak patents in the United States and whether or not the current patent system is capable of correcting weak patent issues. To this end, we propose a new method to identify weak patents by using patent citation information in conjunction with the textual similarity between citing and cited patents. Our method, along with a series of internal validation measures, shows that 13% of U.S. patents filed from 2001 to 2010 are weak patents. By applying this new method, we find that patent owners build a patent portfolio around a weak patent by developing subsequent inventions more than they do for a non-weak patent. Our further analysis finds that a weak patent is more or equally likely to be retained by the patent owner than a non-weak patent. Our findings suggest that patent owners have an incentive to invest in maintaining and appropriating weak patents, and thus, the current patent system is incapable of self-correcting weak patent issues.