How does a two-way test differ from a one-way test in double patenting analysis?

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.

In double patenting analysis, the one-way test and two-way test are used to determine if claims in different applications or patents are patentably distinct:

• One-way test: The examiner compares the claims of the application under examination to the claims of the other application/patent.
• Two-way test: The examiner performs the one-way test and then reverses the analysis, comparing the claims of the other application/patent to the claims under examination.

According to MPEP 804.02, “If a “two-way” test is to be applied, […] the examiner must determine if (i) the first-filed application claims are anticipated by, or obvious in view of, the claims of the second-filed application and (ii) the claims of the second-filed application are anticipated by, or obvious in view of, the claims of the first-filed application.”

The two-way test is generally used when the applications have different effective filing dates and were filed by the same inventive entity.