As a reminder, here is how I measure a team's strength of schedule for a season, (with an adjustment of including four new teams this year, making the total of 124 NCAA FBS schools, instead of 120 as when I originally wrote the blog post). For conference strength of schedule, I take each team's individual strength of schedule within one conference and average of all of those strength of schedules to find the conference strength of schedule. For example, let's suppose the four independent's were a "conference", then for Army, BYU, Navy and Notre Dame I am taking the average of each of the four schools individual strength of schedule measures to calculate their conference SOS.
The "league" as a whole has an average strength of schedule of 65.53, and a standard deviation of 9.55. The reason that the "league" average SOS is it not equal to 62.50 - which would be the average of 1 through 124, since there are currently 124 NCAA FBS schools - is because NCAA FBS teams play teams in the football championship subdivision (FCS) and I do not have a model to rank them, so each FCS school is given a rank of #125 for the season. Given the number of FCS schools on FBS teams schedule, the average for all FBS schools increases to 63.53 from 62.50, which is not that much of a difference.
Here are the results - with the SEC having the most difficult strength of schedule for the 2012-13 NCAA FBS season.