Kristian Ferrell
Wins Above Bubble (WAB) is a system used to rank college basketball teams. It is a way of evaluating the strength of a team's performance by looking purely at wins and losses, rather than attempting to predict future results. WAB calculates the expected winning percentage for an average bubble team in each game of a team’s schedule and then subtracts that total from the team’s actual number of wins. For example, if an average bubble team playing against Team X’s schedule would have won 18 games, but Team X only won 17 games, they would have a WAB of -1. WAB is used alongside other ranking systems such as the AP Poll, RPI, NET, and Her Hoop Stats Ratings.
| Characteristics | Values |
|---|---|
| Purpose | Analyse the strength of a team's résumé based on wins and losses |
| Calculation | Expected winning percentage for an average bubble team in a schedule – the team's actual number of wins |
| Formula | Bill James' Pythagorean expectation formula |
| Exponent | 10 |
| Log5 | Used to generate win probabilities for each game of the season |
| Rating | Her Hoop Stats Rating |
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What You'll Learn
Calculating win probabilities
Wins Above Bubble (WAB) is a method of evaluating the strength of college basketball teams. It calculates the expected winning percentage for an average bubble team in each game of a team's schedule and then subtracts that from the team's actual number of wins. For example, if an average bubble team would have won 18 games against Team X's schedule, but Team X only won 17 games, they would have a WAB of -1.
To calculate win probabilities, the first step is to determine how many points each team scores or allows per 100 possessions, adjusted for strength of schedule. This can be done using offensive and defensive ratings. These ratings are then used to calculate each team's probability of beating an average team. Bill James' Pythagorean expectation formula can be used here. This formula was originally a tool for baseball but has since been adapted for other sports. For college basketball, an exponent of 10 works best.
Once we have an expected winning percentage for each team, we can use log5 (another method from Bill James) to generate win probabilities for each game of the season. For each game, we want to find the probability that a typical bubble team would win that game at that location. To simplify, we can use the 40th-best team as our typical bubble team and calculate the probability that this team would have won each game.
Finally, we can award or revoke credit from a team based on whether they won or lost the game. This allows us to calculate each team's Wins Above Bubble.
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Using Bill James' Pythagorean expectation formula
The Pythagorean expectation formula, also known as the Pythagorean Win Expectation, was devised by Bill James in the 1980s while working as a night watchman at a bean cannery. The formula was originally designed to estimate the number of games a baseball team was expected to win based on the number of runs they scored and allowed.
The formula is as follows:
> Win Ratio = (runs scored^2) / (runs scored^2 + runs allowed^2) = 1 / (1 + (runs allowed / runs scored)^2)
The expected number of wins is then calculated by multiplying the expected winning ratio by the number of games played.
The Pythagorean expectation formula has since been adapted for use in other sports, including basketball, where it can be used to calculate the expected winning percentage of a team based on the number of points they score and allow per 100 possessions, adjusted for the strength of their schedule. An exponent of 10 works best for college basketball.
Once the expected winning percentage for each team is calculated, another Bill James method, log5, can be used to generate win probabilities for each game of the season. This involves calculating the probability that a typical bubble team would win a game at a specific location. The last step is to award or revoke credit to a team based on whether they won or lost the game.
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Ranking teams by WAB
Wins Above Bubble (WAB) is a system that has gained popularity in ranking men's college basketball teams. It is an objective measure of a team's performance strength, analysing their wins and losses rather than attempting to predict future results.
WAB calculates the expected winning percentage for an average bubble team in each game of a team's schedule and then subtracts that from the team's actual number of wins. For example, if a bubble team is expected to win 75% of their games, they are expected to, on average, come away with 0.75 wins. If the team wins, they will have 1 win, which is 0.25 more wins than expected. Conversely, if they lose, they will have 0 wins, which is 0.75 wins fewer than expected.
The first step in calculating WAB is to determine how many points each team scores or allows per 100 possessions, adjusted for the strength of their schedule. This can be done using offensive and defensive ratings. These ratings are then used to calculate the probability of a team beating an average team, using Bill James' Pythagorean expectation formula, which was originally a tool for baseball but has since been adapted for other sports.
WAB rankings are updated regularly throughout the season, and each team's winning percentage above bubble is included. This accounts for the difference in the number of games played by each team, ensuring that teams are not penalised for having fewer opportunities to accumulate wins.
By ranking teams using WAB, it is possible to identify the teams most deserving of making the tournament based on their proven results. This provides a different perspective from other ranking systems, such as the AP Poll, which relies on the opinions of media members, or the Her Hoop Stats Ratings, which use machine learning to predict outcomes.
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Using WAB to inform seeding and matchups
Wins Above Bubble (WAB) is a metric used to evaluate the strength of college basketball teams. It is designed to measure how much better a team's performance is compared to a team that is on the cusp of making a tournament. WAB can be used to inform seeding and matchups by providing an objective measure of a team's strength.
WAB is calculated by first determining the expected winning percentage for an average bubble team in each game of a team's schedule. This is done by considering the number of points each team scores or allows per 100 possessions, adjusted for the strength of their schedule. Then, this expected winning percentage is compared to the team's actual number of wins. The difference between the two values is the team's WAB.
For example, if an average bubble team is expected to win 18 games against a certain schedule, but a particular team wins 20 games against that schedule, their WAB would be +2. A positive WAB indicates that a team has performed better than expected, while a negative WAB indicates that a team has underperformed relative to a bubble team.
WAB can be used to inform seeding and matchups by ranking teams based on their WAB values. This allows tournament organizers to seed teams based on their proven results, rather than solely relying on win-loss records or subjective opinions. By using WAB, organizers can create matchups that are more balanced and competitive, as teams are seeded based on their actual performance relative to the difficulty of their schedule.
Additionally, WAB can help identify potential underdog teams that may have flown under the radar due to a weaker schedule. These teams may have a high number of wins but a low WAB, indicating that their success is not solely due to their skill but also a result of an easier schedule. By considering WAB, tournament organizers can make more informed decisions about seeding and matchups, creating a more exciting and unpredictable tournament.
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WAB in relation to other metrics
Wins Above Bubble (WAB) is a metric used in basketball to measure how much better a team's performance is compared to a team that is on the cusp of making a tournament. It is calculated by determining the number of wins a bubble-quality team is expected to achieve against a given schedule and then comparing it to the actual number of wins achieved by a team. This results in a WAB value that indicates how many more or fewer wins the team has achieved relative to the expected performance of a bubble team.
WAB is similar to the concept of Wins Above Replacement (WAR) used in MLB statistics, which evaluates a player's value in terms of team wins contributed compared to a league-average replacement player. WAB, on the other hand, focuses on the team's performance relative to a bubble team, which is a team that is on the borderline of qualifying for a tournament.
WAB has gained popularity in college basketball due to the difficulty of ranking a large number of teams fairly. Other ranking systems such as the AP Poll, RPI, NET, and Her Hoop Stats Ratings each have their own unique methods for ranking teams. WAB provides an objective measure of a team's performance by analyzing the strength of their résumé based purely on wins and losses, adjusted for the strength of their schedule.
While WAB offers valuable insights, it is important to consider its limitations. Each bubble team has different strengths and weaknesses, and the matchup dynamics in basketball can significantly impact the outcome of games. Therefore, different bubble teams may have varying chances of winning the same game. WAB also does not consider scoring margins or preseason rankings, which may be important factors in evaluating team performance. Nonetheless, WAB serves as a useful tool for comparing teams' schedules and their performance relative to expectations.
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Frequently asked questions
Wins Above Bubble is a metric used to evaluate the strength of college basketball teams. It calculates the expected winning percentage for an average bubble team in each game of a team's schedule and then subtracts that from the team's actual number of wins.
First, calculate the expected number of wins for a bubble-quality team against a given team's schedule. Then, compare this to the number of games that team actually won. The difference between these two numbers is the Wins Above Bubble.
A bubble team is a team that is on the cusp of making it into a tournament.
Suppose a bubble team is expected to win 10 games out of 20 against a certain schedule of opponents. If a team playing that schedule wins 15 games, their Wins Above Bubble is +5. If they win only 5 games, their Wins Above Bubble is -5.
