Rating percentage index
The Rating Percentage Index (RPI) is a quantitative metric employed by the National Collegiate Athletic Association (NCAA) to evaluate and rank teams across various Division I sports, calculating a composite score from three weighted components: a team's own winning percentage (25% of the index), the average winning percentage of its direct opponents (50%), and the average winning percentage of those opponents' opponents (25%).[1] Developed in 1981, the RPI was initially introduced to supplement subjective judgments in selecting at-large teams and seeding participants for NCAA tournaments, with a particular emphasis on accounting for strength of schedule beyond simple win-loss records.[2] While it became a cornerstone of men's college basketball selection until 2018—when it was supplanted by the more nuanced NCAA Evaluation Tool (NET) that incorporates factors like game location and efficiency margins—the RPI remains in active use for sports such as baseball and soccer to inform postseason qualifications and bracket assignments.[3] Over the years, the formula has undergone refinements, including a 2005 adjustment to penalize teams for scheduling weak non-Division I opponents and a 2013 revision for baseball that adjusted win values based on home (0.7) versus road (1.3) games to better reflect performance context.[4] Despite criticisms for overemphasizing certain scheduling patterns and underweighting margin of victory, the RPI's simplicity and focus on schedule strength continue to make it a foundational tool in collegiate athletics ranking systems.[5]Overview and History
Definition and Purpose
The Rating Percentage Index (RPI) is a formula-derived metric used to rank sports teams quantitatively by integrating a team's performance with the strength of its schedule. It combines three primary elements: the team's own winning percentage (WP), weighted at 25%; the average winning percentage of its opponents (OWP), weighted at 50%; and the average winning percentage of those opponents' opponents (OPOP), also weighted at 25%. This structure provides a composite score that reflects both direct results and indirect schedule difficulty, producing a value between 0 and 1 where higher scores indicate stronger teams.[6] The primary purpose of the RPI is to facilitate objective decision-making in competitive sports, particularly within NCAA Division I programs, by aiding in tournament selections, seeding, and evaluations of schedule strength without relying on subjective judgments. It helps selection committees identify at-large qualifiers and determine bracket placements by accounting for the quality of competition faced by each team, thereby promoting fairness across diverse conference structures.[7] First implemented in 1981 for men's basketball tournament selections, as of 2025, while it has been replaced by the NET metric in basketball since 2018 for more advanced analytics, the RPI remains in use for NCAA sports such as baseball and lacrosse to support similar ranking and selection processes.[8][6][9]Origins and Adoption
The Rating Percentage Index (RPI) was developed in 1980 by NCAA statistician Jim Van Valkenburg and the Division I Men's Basketball Committee as an objective metric to mitigate subjective biases in tournament team selections, where prior rankings relied heavily on polls and human judgment.[10][11][12] This initiative stemmed from growing concerns over the expanding NCAA tournament field and the need for a data-driven supplement to evaluate team strength based on wins, losses, and schedule difficulty.[13] The RPI received its first formal adoption in 1981 for selecting at-large bids and seeding teams in the NCAA Division I men's basketball tournament, marking a shift toward incorporating quantitative analysis in postseason decisions.[13] It quickly became a standard tool, providing the committee with a consistent framework to compare teams across conferences. The women's basketball committee followed suit in 1984, integrating RPI into their selection process.[14] Over the following decades, the RPI expanded beyond basketball to other NCAA sports, beginning with baseball in 1984 to aid in regional seeding and at-large selections.[15][16] By the early 2000s, it was adopted for soccer, with regular RPI rankings released starting around 2006, and for lacrosse, with first official rankings in 2010, where it helped standardize evaluations for championship fields amid varying conference schedules.[17][18][19] Football saw limited application in lower divisions by the late 2010s, though major playoff selections primarily used alternative metrics.[20] A significant milestone occurred in 2018, when the NCAA introduced adjusted RPI formulas across multiple sports—excluding basketball, which transitioned to the NCAA Evaluation Tool (NET)—to refine home/away win valuations and reduce scheduling incentives.[13] These modifications aimed to enhance fairness without overhauling the core methodology. As of 2025, RPI remains in use for non-Division I contexts, including Division II and III championships in sports like baseball and soccer, supporting ongoing tournament selections.[9][21]Core Components and Calculation
Key Elements
The Rating Percentage Index (RPI) relies on three core components to evaluate team performance relative to schedule strength: the team's winning percentage (WP), opponents' winning percentage (OWP), and opponents' opponents' winning percentage (OPOP). These elements form the foundational building blocks of the index, emphasizing both direct results and contextual factors like opponent quality.[6] The winning percentage (WP) serves as the baseline measure of a team's performance, calculated as the ratio of wins to total games played, with ties treated as half a win and half a loss where applicable. In NCAA implementations, WP is adjusted for game location to better reflect performance context, weighting home wins and road losses at 0.6, road wins and home losses at 1.4, and neutral-site games at 1.0 (with slight variations, such as 0.7/1.3 for baseball).[6][14][4] Opponents' winning percentage (OWP) gauges the strength of a team's schedule by averaging the winning percentages of all opponents faced, adjusted to exclude games played against the team in question. This adjustment ensures an unbiased assessment of opponent quality, focusing on their performance in other contests to reflect the overall competitiveness of the schedule.[6][14][4] Opponents' opponents' winning percentage (OPOP) extends this evaluation by averaging the OWP values of the team's opponents, thereby capturing the indirect quality of the schedule through the opponents' own scheduling challenges. This layer accounts for broader competitive ecosystems, rewarding teams that face opponents with strong slates of games.[6][14][4] In the RPI formula, these components are typically weighted with WP contributing 25%, OWP 50%, and OPOP 25%, though variations exist across sports to adapt to specific competitive dynamics.[14][4]Step-by-Step Computation
The Rating Percentage Index (RPI) is calculated using a multi-step process that incorporates a team's performance and the strength of its schedule, based on winning percentages derived from game outcomes. This generic computation applies across sports like basketball and baseball, with specific weights determined by the context of application. The process begins with determining the team's own winning percentage and then extends to the winning percentages of opponents and their opponents, excluding the influence of games against the team in question to avoid circularity.[22]- Calculate the team's Winning Percentage (WP): Divide the number of wins by the total number of games played, with ties treated as half a win and half a loss: WP = (wins + 0.5 × ties) / total games. In NCAA RPI, this is an adjusted winning percentage, where wins and losses are weighted by game location (e.g., home wins at 0.6, road wins at 1.4, neutral at 1.0; baseball uses 0.7/1.3). This provides a baseline measure of the team's direct performance adjusted for context.[23][4]
- Calculate the Opponents' Winning Percentage (OWP): For each opponent the team has faced, compute that opponent's WP, but exclude any games played against the team being evaluated. Average these adjusted winning percentages across all opponents to obtain OWP, which assesses the strength of the team's schedule.[14]
- Calculate the Opponents' Opponents' Winning Percentage (OOWP or OPOP): For each of the team's opponents, compute the OWP of that opponent's opponents (again, excluding games involving the original team). Average these values across all of the team's opponents to yield OOWP, which further refines the schedule strength by considering the broader competitive environment.[24]
- Combine the components into the RPI: Apply a weighted average using the formula \text{RPI} = w_1 \times \text{WP} + w_2 \times \text{OWP} + w_3 \times \text{OOWP}, where w_1 + w_2 + w_3 = 1 and the specific weights vary by application (e.g., emphasizing schedule strength over team performance in some contexts). Location-based adjustments apply only to the WP component, not to OWP or OOWP.[14][23][4]