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By law, an issued U.S. patent is presumed valid in court. While Congress placed the burden of establishing a patent’s invalidity on the challenging party, it failed to specify the particular quantum of proof necessary to overcome this presumption. In a 2011 decision, Microsoft Corp. v. i4i Limited Partnership, the Supreme Court held a patent’s invalidity must be established by clear and convincing evidence. However, a jury may be instructed that prior art not previously considered by the U.S. Patent and Trademark Office (USPTO) can assist the challenger in satisfying its burden. Several recent empirical studies have sought to assess the impact of the presumption of validity following Microsoft v. i4i. These studies generally find that the clear-and-convincing evidence standard can have a material impact on invalidity decisions in litigation. In addition, these studies suggest that invalidity challenges based on prior art not previously considered by the USPTO are more likely to succeed.