What standard of proof is used in patent examination?

This page is an FAQ based on guidance from the Manual of Patent Examining Procedure. It is provided as guidance, with links to the ground truth sources. This is information only: it is not legal advice.

The standard of proof used in patent examination is the “preponderance of the evidence” test. The MPEP states:

“The standard to be applied in all cases is the ‘preponderance of the evidence’ test. In other words, an examiner should reject a claim if, in view of the prior art and evidence of record, it is more likely than not that the claim is unpatentable.”

This means that examiners must determine if it is more probable than not that a claim is unpatentable based on the available evidence and prior art.