The Court of Appeals for the Federal Circuit held that the quantum of proof for priority is clear and convincing evidence, and that corroboration of inventor's testimony will be evaluated by the "rule of reason."
Price v. Symsek, 988 F.2d 1187 (Fed. Cir. 1993).
Warren M. Haines II,
Intellectual Property - Patent Law - Interferences,
Duq. L. Rev.
Available at: https://dsc.duq.edu/dlr/vol32/iss1/6