# Mathletics: How Gamblers, Managers, and Sports Enthusiasts Use Mathematics in Baseball, Basketball, and Football

By Wayne Winston | Go to book overview

42
THE RATINGS PERCENTAGE INDEX (RPI)
During the college basketball season hoop fans anxiously anticipate the selection and seeding of teams for the NCAA tournament. The NCAA selection committee wants an accurate view of the teams' relative abilities, but, like the BCS selection committee, the NCAA tournament selection committee wants to use only a team's win- loss record and not the score of their games to rank teams. The NCAA believes that including game scores in the ranking and seeding pro cess would cause the top teams to try and run up the score on lesser opponents. In chapter 40 we explained how to use a logistic regression- based ranking system to rank NFL teams. An identical system would do an excellent job of ranking college basketball teams. Defying logic, however, the NCAA uses the complex and flawed Rating Percentage Index (RPI) to rank college basketball teams.Let's suppose we want to compute the RPI of Indiana University (IU). IU's RPI ranking is computed as a weighted average of three quantities:
 • IU's own winning percentage (referred to as TWP). • Not counting the games involving IU, the winning percentage of each of IU's opponents. These winning percentages are averaged to compute OPP = opponent's average winning percentage. • OPPOPP = the average winning probability of IU's opponents' opponents (not including games in which they play any of IU's opponents but including games played against IU).

The home team in college basketball wins around 70% of the games between equally matched teams. This gave teams like Duke, which played many more home games than road games, an unfair advantage in the RPI rankings. Beginning with the 2005 season, a home win or road loss was counted as 0.6 wins or 0.6 losses. An away win or home loss was counted

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