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This study compares 438 patents that had invalidity determinations made by both the Patent Trial and Appeal Board (PTAB) and district courts. The PTAB and court agreed on 53% of the patents and disagreed on 47%. When they disagreed, the district court took the side of the inventor 4 times as often as the PTAB (39% to 8%).
Notably, district courts allow challenges under §101 (eligibility), §102 (novelty), §103 (obviousness), and §112 (written description and enablement). PTAB typically only allows §102 and §103, yet with only two grounds they go against the inventor 4 times as often as the district court. So the discrepancy is even worse than this indicates.
Another way of looking at it is the PTAB invalidated 79% while the district court invalidated 48% of these patents that were reviewed in both venues.