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ABOUT THE CPI
The CPI (Comparative Performance Index) reflects the strength of team performance during a season by balancing a team's record with those of its opponents, independent of the team. The formula is designed to be clear and intuitive, with accurate, sensible results.
Similar to the NCAA's RPI, teams are rated using only the win percentages of themselves and their opponents. The formula rates each team according to the following:
[ CPI Rating = W%3 × Ow%2 × Oow%1 ]
where W% is the team's win percentage,
Ow% is the team's opponents' win percentage independent of the team, and
Oow% is the team's opponents' opponents win percentage independent of the team's opponents.
All percentages are taken as the sum of wins over the sum of games played. The design gives greater importance to games closer to a team's circle of competition, balances a team's record equally with its schedule, is unbiased, and makes no arbitrary adjustments.
To account for non-FBS competition, the final rating is the greater of two calculations, one which includes all games played, including FCS opponents and opponents' opponents, and one which ignores results of games between FCS level competition. This eliminates negative distortion from results outside of FBS competition. FCS ratings also exclude results of games outside of FCS competition.
The results are strongly aligned with polls of college football experts and more complex computer algorithms. By compounding the win percentages through multiplication, the CPI creates a more accurate rating while maintaining the common sense intuition of a formula like the RPI.
Ratings and percentages from past years can also be compared in a consistent way with today's top teams, for insight into the shape of the college football landscape and the quality of title contenders.
Importantly, the system is transparent. Ratings are listed with wins and losses, win percentages, and the team's strength of schedule ranking. Readers can see exactly how each team is ranked on the basis of their record, and can judge the legitimacy of each ranking. The ratings are also verifiable through the CPI's open formula.
The CPI has matched the top two teams for the BCS title game in thirteen of sixteen years, putting it on par with BCS computers and polls in aligning with the BCS standings for the title matchup. The CPI also aligns well with the 25-team BCS Standings throughout a given season.
The CPI does not take into account margin of victory, location, or any measure other than win percentage in its calculation.
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