Better accounting for FCS opponents
Most college football fans would acknowledge that playing four-time reigning FCS champion North Dakota State is not nearly the same as facing a bottom-tier FCS team. The Bison have won five straight games against FBS opponents dating to 2010, including four straight against Power 5 teams. That’s as many Power 5 wins as Kansas has since 2010!
So when North Dakota State headed to Iowa State last season, it was clear to the average fan that the Cyclones were not facing a typical FCS opponent. In the previous iteration of FPI, however, all FCS teams were regarded as being of the same caliber and rated below the weakest FBS team. Based on that logic, Iowa State entered the game with a 97 percent chance to win, and when they lost 34-14, the Cyclones fell 31 spots in FPI.
In a small 12-game sample, misrepresenting the actual strength of even one opponent could have a significant impact on a team’s FPI, which has a trickle-down effect on a number of FPI’s outputs -- such as future game projections and strength of schedule.
From the moment FPI was released in 2013, we knew this was a problem that had to be solved, but because of limitations with FCS data, we rolled out FPI with the intention to resolve this issue in the future.
Today, each FCS team has an FPI rating based on the final score of games dating back four years. As with FPI for FBS teams, the rating is a measure of team strength and represents the expected scoring margin against an average FBS opponent.
For example, North Dakota State enters the season with an FPI rating of plus-0.9, meaning if the Bison were to play an average (or 64th-ranked) FBS team, they would be favored slightly on a neutral field. In the coming season, there are 32 FCS teams with a higher FPI rating than the weakest FBS team and seven FBS-vs.-FCS games in which the FCS team has at least a 25 percent chance to win.
By capturing the true strength of each FCS team, we are also improving the accuracy of FPI’s FBS ratings and game predictions. With the updated formula, the team FPI favored continued to win 75 percent of FBS-only games since 2005, but predicted scoring-margin errors decreased compared with the previous system.
After accounting for the relative strength of FCS teams, Iowa State entered its home game against North Dakota State with a 66 percent chance to win. After losing to the Bison, the Cyclones fell 15 spots in FPI, and what was once a historically crippling loss was treated no differently than a loss to about the 66th-ranked FBS team.
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