# Rating Percentage Index

## What is the Rating Percentage Index in Basketball?

The Rating Percentage Index (RPI) is a statistical method used to rank sports teams based on their performance and the strength of their schedule. It is primarily associated with college sports, such as NCAA basketball, baseball, softball, hockey, soccer, lacrosse, and volleyball teams. Developed in 1981, the purpose of RPI is to provide an objective measure for comparing teams and assisting the selection committee in making decisions for championship tournaments.

RPI considers three main factors when calculating a team’s ranking. First, it assesses the team’s winning percentage against Division I opponents, which accounts for 25% of the RPI score. Second, it evaluates the team’s opponents’ winning percentage, or strength of schedule, at 50% of the RPI. Lastly, the remaining 25% of RPI comes from the team’s opponents’ opponents’ winning percentage, or the opponents’ strength of schedule.

By taking into account both wins and losses and the difficulty of a team’s schedule, the RPI ranking system offers a fair and balanced method for evaluating the overall performance of teams within their respective sports. This helps to create a more accurate representation of a team’s quality and facilitates informed decisions by championship selection committees.

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## Definition and Purpose of RPI

The Rating Percentage Index (RPI) is a metric used to rank sports teams based on a team’s wins, losses, and the strength of their schedule. RPI is mainly utilized in NCAA sports such as basketball, baseball, softball, hockey, soccer, lacrosse, and volleyball.

The primary purpose of RPI in basketball is to assist NCAA selection committees in selecting at-large teams and seeding all teams for the men’s and women’s NCAA basketball tournaments. Essentially, the RPI helps determine which teams are deserving of a spot in the prestigious tournament based on their performance and the quality of their opponents.

### Calculating RPI

There are three factors that contribute to a team’s RPI score:

1. Team’s winning percentage: This is the ratio of games won by a team to the total games played.
2. Opponents’ average winning percentage: This is the average winning percentage of all the teams that a specific team has played against.
3. Opponents’ opponents’ average winning percentage: Also known as the strength of schedule, this is the average winning percentage of the teams that a specific team’s opponents have played against.

The formula for calculating RPI is as follows:

`RPI = (0.25 * Team's Winning Percentage) + (0.5 * Opponents' Average Winning Percentage) + (0.25 * Opponents' Opponents' Average Winning Percentage)`

### Components of RPI

RPI focuses on the following aspects to determine a team’s ranking:

• Wins and losses: A team’s win-loss record is a crucial component of RPI. It accounts for 25% of the RPI score.
• Strength of schedule: The quality of a team’s opponents is a crucial aspect of RPI. It considers both the opponents’ average winning percentage (50% of the RPI score) and the opponents’ opponents’ average winning percentage (25% of the RPI score).

By combining these aspects, the RPI provides a comprehensive ranking metric that takes into account not only a team’s performance but also the difficulty of the competition they faced. This helps selection committees make informed decisions when deciding which teams deserve a spot in the NCAA tournament.

## Impact and Usage of RPI

### Influence on Team Selection and Seeding

The Rating Percentage Index (RPI) has been a significant tool in college basketball for evaluating teams based on their wins, losses, and strength of schedule. Introduced in the early 1980s, RPI has been employed by the NCAA Selection Committee to help determine which teams are granted at-large bids and how they are seeded in the NCAA Tournament.

This metric facilitates a more equitable comparison between teams by considering not only their performance but also the quality of their opponents. As part of RPI’s calculations, the following factors are taken into account:

1. Team’s winning percentage: accounts for 25% of the RPI score
2. Opponents’ average winning percentage: contributes 50% of the RPI score
3. Opponents’ opponents’ average winning percentage: makes up the remaining 25% of the RPI score

### Criticism and Limitations

Despite its long-standing usage, the RPI system has faced criticism and is acknowledged to have certain limitations. One major issue with RPI is its lack of transparency, as the NCAA did not initially make the RPI available to member institutions or the public during the season. Additionally, critics argue that RPI inadequately represents key performance indicators, such as margin of victory or efficiency statistics.

In response to these concerns and to adapt to newer analytics, the NCAA replaced RPI with the NCAA Evaluation Tool (NET) in 2018. The NET system takes into account game results, strength of schedule, game location, scoring margin, net offensive and defensive efficiency, and the quality of wins and losses, thus providing a more comprehensive evaluation of teams.

Despite its limitations and eventual replacement, RPI’s impact on college basketball cannot be understated. For many years, it served as a foundation for team comparisons, seeding, and tournament selections and influenced the evolution of sports analytics in basketball.