According to a post on the blog, fivethirtyeight.com
http://fivethirtyeight.com/features/how-much-college-quarterbacks-are-worth/
This is an interesting look at all the QB's for the last nine years in college football.
it basically uses ESPN's QBR and a measure called "school-fixed effects" to determine a baseline for the school and he level of quarterback play for each school.
If the publisher of this blog wasn't so good at making observations and prognostications I would probably question more of the numbers but I think they typically do a good job of thinking this stuff through.