Prior Art in the District Court

This Article is an empirical study of the evidence district courts rely upon when invalidating patents. To construct our dataset, we collected every district court ruling, verdict form, and opinion (whether reported or unreported) invalidating a patent claim over a six-and-a-half-year period. We then coded individual invalidity rulings based on the prior art supporting the court’s decision, observing 3320 invalidation events relying on 817 distinct prior art references. The nature of the prior art relied upon to invalidate patents is relevant to two distinct sets of policy questions. First, this data sheds light on the value of district court litigation as an error- correction tool. As prior work has shown, the public interest in revoking erroneous patent grants depends on the reason those grants were undeserved. Second, this data sheds light on the feasibility of discovering invalidating prior art during patent examination. Depending on the ease of finding the relevant prior art, it may or may not be cost effective to replace patent litigation with a different approach to error correction, such as investing more effort in examination-stage scrutiny. The conclusions here are mixed. On one hand, invalidations for lack of novelty bear many indicia of publicly beneficial error correction. Anticipation based on obscure prior art appears to be quite rare. When it comes to obviousness, however, a significant number of invalidations rely on prior art that would have been difficult or impossible to find at the time of invention. This complicates—though does not necessarily refute—the traditional view that obviousness challenges ought to be proactively encouraged.