On May 5, USCIS announced changes to how it communicates case processing data to the public. Previously, USCIS displayed case processing times as the amount of time it took USCIS to approve or deny a certain percentile of completed cases over the prior six-month period. After this policy change, USCIS will display processing time information for their particular case rather than an aggregate of all related case types. USCIS will also make additional changes to case processing times, including the ability to narrow results and a case inquiry tool specific to the individual case.
More information can be found here.