For those curious:
“Total QBR was developed by a team at ESPN Stats & Information Group including Jeff Bennett, Dean Oliver, Alok Pattani, Albert Larcada, and Menlo College professor Ben Alamar. The group also received input from ESPN analysts Trent Dilfer, Jon Gruden, and Ron Jaworski. Total QBR was developed based on analysis of 60,000 NFL plays between 2008-2010, and was unveiled on August 5, 2011. The formula was modified in 2012 and again in 2013.”