Advanced Patent IndeX (APIX) is an internally developed tool to measure patent validity. APIX uses a machine learning algorithm to rate the chances the PTAB may institute on a patent based on its similarity to all past institution decisions. Patents are ranked from D (least likely) to AA (most likely) to survive a PTAB challenge. The most important result from APIX was that PTAB has instituted more often on patents from examiners and art units with a higher allowance rate. For more information on the complete variables results contact Unified Patents.
To come up with the APIX rating, a raw score is generated for all US patents. Patents are then rated based on how many standard deviations they are from the mean.
For example: an "A" APIX score means that patent is in the top 16% of all patents for validity. But given the institution rate, an "A" APIX score means it has an almost 50% chance of being instituted on if challenged.