The Math
CFB Power Digits is a completely unbiased mathematical way of ranking teams in College Football.
The primary objective of this ranking is to not necessarily predict future winners, but to determine who has the best resume for College Football Playoff and New Year’s Six selections. However, it does very well in predicting winners.
The Rankings were built to give a non-biased approach to teams’ strengths. By defining the path to success before the season, no name-bias will help a team’s ranking. The Power Digits methodology does come from the beliefs of the creator, Stephen Polacheck, and what he believes should help teams qualify for the College Football Playoff.
There is no *right* way to rank college football teams. This is simply one way to do it, which will sometimes agree with the Pollsters and CFP, but other times not.
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Every FBS 1-A team is given a Power Digits Rating, a number between 0 and 1, which determines their rank. 1 is the best possible value a team can have, 0 being the worst.
The algorithm is broken up into 5 different components. These are Team W-L Rating, Strength of Wins, Strength of Losses, Strength of Schedule, and Top 3 Wins.
The base of the algorithm is in the Team W-L Rating, which makes up 60% of the rating. Within this 60%, half of the rating is the teams weighted win percentage, the other half being that of their opponents.
A weighted win percentage comes from giving more (or less) than 1 into a win/loss column. Based on conference and location of the opponent, these values change. See the following chart for the breakdown. The numbers are not arbitrary, they come from a formula to determine conference strengths.
Conference strengths come from the win percentage of the conference over the last two seasons in all FBS-FBS games (including bowls), removing in-conference and FCS games. Then, if the conference is a “Power 5” conference, 0.55 is added to the base number. If the conference is a “Group of 5”, 0.45 is added. This number becomes the value of a neutral site win against a team from that conference. If the win was on the road, 0.05 points are added, if it was at home, 0.05 points are subtracted.
For losses, the conference strength is 2 minus the conference value. This means losing to teams from the best conference count for less than 1 loss. Like the wins, this is the base value, factored at a neutral site. A loss on the road takes 0.05 away from the loss, if it was at home, 0.05 is added.
50% of the W-L rating comes from the team’s weighted win percentage, and then another 50% is the combined weighted win percentage of their opponents. Teams are benefitted when their previous opponents win games.
5% comes from the strength of wins, which is the combined win-loss rating of the teams that were beaten. If the team is winless, they receive a 0.
Another 5% come from the combined win-loss rating of the teams lost to. If a team is undefeated, they receive a 1.
15% comes from the overall strength of schedule. This is the combined weighted win percentage of all the opponents that they faced.
The last 15% come from the average win-loss ratings of the 3 best teams beaten. This is meant to reward those who have played multiple strong opponents, and not to be carried by playing (and losing to) tough opponents.
In addition, an extra bonus is awarded to conference champions. Taking the same values as outlined above, divided by 100, and added to the Power Digits score. For example, Alabama (2020 SEC Champion) is awarded a bonus 0.0128.
Again, these ratings are not meant to say “Team X is better than Team Y,” they say “Team X deserves a playoff spot before Team Y does.”
Frequently Asked Questions
Why do the rankings look so "wrong" for the first few weeks?
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The rankings benefit from more games, it learns from more results. During week 1, it may only know that Maryland is better than Eastern Michigan, but by week 2, 3, 4, when Maryland has beaten/lost to other opponents, it continues to factor in the success of Eastern Michigan. As Eastern Michigan wins games, Maryland receives bumps to their ratings, and as the season grows, the network of opponents grows as well. By the time we reach week 12, Maryland has 10 opponents each with their own 10 wins and losses, and this builds up the strength of schedule part of the rating.
If we know Alabama is better than Akron, why do they start​ with no rank advantage?
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We as fans may think we know that Alabama will be better than Akron, but it must be proven on-field. The rankings are based on only the data from the season in question, so there are no pre-conceived biases. College football team success is volatile, Michigan State went 12-2 with a playoff appearance in 2015, followed up with a 3-9 record in 2016. For reasons like this, the Power Digits gives no credit or punishment to teams based on previous seasons. The start of every year is a blank slate. Do we really know Alabama is better than Akron, or are we just guessing on recency bias?
Do teams who go undefeated against easy opponents get ranked higher because of win percentage?
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No, because the Power Digits Rating holds a high weight to Strength of Schedule. Teams will benefit from being undefeated, yes, but over 40% of their ranking will be hampered by them having weak opponents.
Do Group of 5 teams benefit from the Power Digits?
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No, they don't. They actually have it harder, as their conference games hurt their win percentages. A win against another Group of 5 is worth less than an average 1 win, and a loss is worth more than an average 1 loss. If they are undefeated, they float around the CFP Top 4, but after a loss they very rarely crack the top 10. Because their strength of schedule is usually very low, they need to have an almost flawless season otherwise to crack the Top 10. (Which is how I believe it should be)
How accurate are the rankings to the real life rankings?
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Well, that's for you to decide. This is an independent ranking and should be seen as something different than the AP Poll and the CFP Committee's rankings. There is no 100% accurate way to rank these teams, unless they all played each other in a season. The Power Digits are a bias-free alternate way to rank teams.
So scheduling the worst Power 5 teams is the best way to defeat the algorithm?
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To a point, yes. A win on the road against Rutgers still credits you with more than an average win, and a win on the road at Ohio State credits you the same. For your overall win percentage, yes, it helps you. However, the difference between the Rutgers and Ohio State wins are made up for in the Strength of Wins, and Strength of Schedule categories, where Ohio State success will provide more of a boost, and Rutgers struggles will bring your rating down.
Why do undefeated teams get such a boost?
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They’re undefeated. If nobody that they played were able to beat them, then they should be rewarded. Until a team loses, we can only guess as to how good a team truly is.
Why is there a bonus for Conference Championships?
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Because I believe there should be. Some reward should be given to winning the one title you can for your regular season. It shouldn’t be a requirement to make the CFP, but it should definitely help your resume.
How are Independent teams classified?
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They are classified as the conference they are most closely represented by, or their previous conference. Notre Dame is classified in the ACC, BYU to the Mountain West, and Army to the American.
Have another question that isn't answered here?
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Give a mention to @PowerDigits on Twitter, and a response will be as fast as possible. If deemed to be an unanswered topic, it will be added in the FAQ section on this page.