clock menu more-arrow no yes mobile

Filed under:

Stats Corner: How are the Basketball ranking created?

Looking at the RPI, NET, and KenPom rankings

NCAA Men’s Basketball Tournament- Championship Photo by Mitchell Layton/Getty Images

Beginning in 1981, until to the 2018 basketball season, the NCAA used the RPI system. Beginning with the 2019 season the NCAA use the NET system as a way to ranked the NCAA basketball teams. To say the NET was not well received by certain teams is an understatement, N.C. State Athletic Director Debbie Yow release a statement “Based on the metrics sited above that the NCAA indicated they would use to evaluate team performance, we are disappointed for our athletes, coaches and fans that our total body of work was not rewarded with selection to the NCAA Tournament.” And TCU coach Jamie Dixon said during his press conference “You look at the NET, there are six teams that had a lower NETs than us. They created a tool and talked about it and then there are six teams there that are lower than us that are in.”(read “we are an average Power 5 school we should get in”). In the years since then, the NET system has been changed, but still used. Today, on Stats Corner, we are going to overview the old RPI, the NET, and KenPom and how they ranking the NCAA teams.

RPI

The RPI is a straight win/loss formula used to ranked teams. RPI = (WP * 0.25) + (OWP * 0.50) + (OOWP * 0.25) with WP being Winning Percentage, OWP being Opponents’ Winning Percentage and OOWP is Opponents’ Opponents’ Winning Percentage. The WP is calculated by dividing the number of team wins by the total number of games played and is a quarter of the RPI. The opponents’ winning percentage is half, and the winning percentage of those opponents’ opponents is the final quarter. There is a strength of schedule component which is the OWP and OOWP. Therefore, 75% of the RPI is not how the specific team does, but rather how their opponents have done, or SOS. Currently Utah State is 4th in RPI at 0.663 and San Diego State is 5th at 0.661, while Air Force is 264th at 0.448.

NET

NET is an acronym for NCAA Evaluation Tool and while the NCAA screws up a lot of things, they absolutely got this acronym correct. It is a predictive-learning model. Predictive learning is a method of machine “learning”. The machine attempts to create a model by simulating different outcomes in situations. These situations are numerous, with the computer comparing expected results with actual results and adjusting as needed.

When the NET was introduced, there was five factors it considered: Team value index, Net efficiency, winning percentage, adjusted win percentage, and scoring margin. The team value index considered 3 factors opponent, location, and winner. Net efficiency was team offensive efficiency minus defense efficiency. Adjusted win percentage gave added points for winning on the road and took points away for losing at home, in short where you played mattered. Winning percentage and scoring margin are self-explanatory, only note is scoring margin was capped at 10 points

Also, there are four quadrants based on where your opponent is ranked, you will hear about Quad 1 and Quad 2 records. For example, San Diego State is ranked 21st and is 2-3 in Quad 1 and 3-0 in Quad 4, while Utah State is 24th and is 2-2 in Quad 1 and 5-0 Quad 4. This means that while the Aztecs do have 3 loses, they are to higher caliber teams and will not affect their ranking. The Aggies however, have less Quad 1 losses, but have more Quad 4 games, affecting their ranking. A Quad 1 loss is not a deal killer, or even a Quad 2 loss. The divisions for the quadrants are:

Quadrant 1: Home 1-30; Neutral 1-50; Away 1-75.

Quadrant 2: Home 31-75; Neutral 51-100; Away 76-135.

Quadrant 3: Home 76-160; Neutral 101-200; Away 136-240.

Quadrant 4: Home 161-plus; Neutral 201-plus; Away 241-plus.

Wyoming is ranked 203rd and Fresno State is 231st , so a Fresno State at Utah State is a Q1 for Fresno and a Q4 for Utah State, while Nevada at Wyoming is a Q1 for Wyoming but because is playing away it is a Q3 game, but would be a Q4 game at home. The San Diego State at Boise State is a now Q1 for Boise State and Q2 for San Diego State because Boise is ranked 54, but last week it would have been a Q1 because Boise was ranked 44th . If Boise moves above 50th during the season, it would become a Q1 for the Aztecs.

Starting in 2020, winning percentage, adjusted winning percentage and scoring margin were all dropped from the NET ranking. Therefore, only team value and team value index are used to ranked teams. So, the only factors which go into the rankings are efficiency (offensive points per possession minus opponents points per possession), strength of opponents played, location of game, wins and losses, and who won the game.

KenPom

Created by Ken Pomeroy, the KenPom rankings are independent of the NCAA. He has his own autonomous website. He ranks every NCAA team by adjusted efficiency margin or adjusted offensive efficiency minus adjusted defensive efficiency. Before you say “that’s what the NET system does” two things. First, KenPom came first. Second, it is ADJUSTED efficiency. Team efficiency is how many points are scored per 100 possessions. The adjusted factor for KenPom is based on how many possessions a team has per game. Alabama has the highest offensive efficiency of 125.1 (they would score 125 points per 100 possessions), however they have an adjusted team efficiency of 71.9, meaning they have 71.9 possessions during a 40-minute game which is 36th in the nation. Kennesaw State is the highest at 76.2 possessions per 40 minutes and Virginia is the lowest at 61.1 possessions. Therefore St. Mary’s are more effective with their fewer per game possessions. If you go to KenPom’s website you will see his different metrics he uses going from left to right, we will use the highest ranked MWC, San Diego State #23, as an example.

Adjusted Efficiency Margin (AdjEM): This is the final ranking, everything else go into this. The higher the score the higher ranking. In short, it’s the offensive efficiency minus the defensive efficiency. At 21st the Aztecs have a score of 18.70, which means they would beat an NCAA team by an average of 19 points.

Adjusted offensive efficiency (AdjO) and Adjusted defensive efficiency (AdjD) have been covered. For the Aztecs AdjO is 113.6 (52nd ) and AdjD is 94.9 (22nd).

Adjusted tempo (AdjT): The amount of possessions a team has per game. There is a formula for it: Possessions per game = Field goals attempted - offensive rebounds + turnovers + 0.475 x attempted free throws. This is used to equalize the scores between run and shoot teams with lots of possessions and teams which grind it out and play at a slower pace. San Diego State is at 68.0 which is 192nd in the country, so they place a little slower than the average.

Luck rating: This is your close game factor. Statistically, a team should go .500 in one possession games. The luck rating is the deviation between a team’s actual winning percentage and the expected from the above metrics. If teams are winning more of the close games they are considered “lucky”. The Aztecs are lucky at +.083 which is 50th in the country. FYI, 7-10 Michigan is the unluckiest team in the country at -.165. and 15-1 Mississippi is the luckiest at .178

Strength of Schedule: This is the average AdjEM, AdjO, and AdjD of the opponents. The better the opponents the higher the SOS. San Diego State’s opponents have an AdjEM of 8.83 which is the 12th toughest schedule in the country, as the Aztecs opponents are winning their games by an average of 8 points.

Non-conference strength of schedule (NCSOS): The conference schedule is out of the college’s control, they non-conference schedule is something the college controls. This section is a reward for putting together a more difficult non-conference schedule instead of playing cupcakes. The Aztecs had a good non-conference schedule at 12th with an AdjEM of 9.94. Compared to Air Force who has the 357th NCSOS at -9.48, meaning their non-conference opponents lost by 9 points.

While both methods use similar data, the biggest differences are

1) NET uses game location as a factor in the ranking system, while KenPom does not factor where the game was played in rankings.

2) Ken Pom uses adjusted efficiency based on how many possessions a team has per game while NET uses points per 100 possessions regardless of possession per game.

3) Scoring margin does not matter to the NET, but it does to KenPom.

4) KenPom does not factor wins and losses, it is simply an efficiency number.

5) KenPom uses strict formulas (predictive) to create ranking while NET uses a learning algorithm comparing what is expected to what happens.