RPI – an acronym that gets thrown around a lot in the world of college basketball. Like a lot of things in sports, though, a lot of people talk about it without really understanding what it is, why it matters, the faults it has, and how it can be useful by sports handicappers.
The RPI, which stands for Ratings Percentage Index, is a mathematical calculation used in college basketball to aid in how teams are selected for the NCAA tournament, and where they are seeded once they get there. It doesn’t specifically act as an official tiebreaker or have other specific powers, but it has significant weight nonetheless, and is widely looked at as one of the better ways to compare teams in college basketball. For this reason it can be useful to NCAA basketball handicappers to a limited degree. There is nothing about the RPI that limits it specifically to basketball, though – other sports use it in the college ranks, but if you hear it referred to by the media then chances are they are talking about college basketball.
RPI is a formula that is concerned about just one concept – winning percentage. Specifically, three types of winning percentages – that of the team in question (WP), that of the opponents that that team has played (OWP), and that of the opponents of those opponents (OOWP). The formula is:
RPI = (WP*0.25) + (OWP*0.50) + (OOWP*0.25)
In college basketball a further adjustment was made to the formula to account for the difficulty of winning on the road. For a team’s winning percentage a win at home counts as just 0.6 wins, while a road win counts as 1.4 wins. A home loss counts as 0.6 losses, while a home loss counts as 1.4 losses. Neutral site wins as and losses are unaffected. Those factors are considered only in the WP, not the OWP or OOWP. In all cases, only games against other Division 1 teams are counted.
Sports bettors could theoretically calculate their own RPI, but it is a very complex process. There’s no need to do it because it is widely available on many websites, and is even updated hourly in some places.
The RPI calculation will yield a combined winning percentage, and that is widely available, but it’s not the most important way the numbers are used. What’s far more important is the RPI Rank – how a team’s RPI compares to all of the other teams in Division 1. This tells you how any given team is performing compared to every other team out there. A team with an RPI Rank of 12, for example, is having a much better all round year than a team at 200.
The RPI Rank is even more useful when you use it in context. Because of the significance of the opponents a team has played it is easier for a team from a major conference to have a high RPI than it is for a team from a mid-major. If a college basketball team from a somewhat obscure conference is ranked highly in the RPI, then, you can be reasonably sure that they are a team to take a closer look at. On the other hand, if a team in a major conference is well behind the rest of the teams in the conference in terms of RPI then they are probably struggling badly.
RPI can also be very helpful when combined with a basketball team’s record to get a more accurate sense of the team’s performance than the record alone. If a team has a record at or below .500 after 10 or a dozen games then your first instinct is likely to disregard them as a good team. If that bad record is combined with a high RPI rank, though, then it means that though they have lost more games than is ideal they have been playing strong opponents. That means that they are probably performing better than their record indicates, and they could show that when they play weaker competition. That could help you spot teams that could be surprisingly strong in conference play. On the other hand, if a college team has a very record but a low RPI then they have probably feasted on weaklings, and could be in for a real shock when conference play starts. The betting public loves flashy records, so a team that has a record that doesn’t reflect their real ability is very useful for bettors.
As useful as RPI can be, and as big a role as it plays in determining the tournament field, it is a long way from perfect. Perhaps the biggest problem that it has is that it doesn’t factor in how teams win, which is something expert college basketball handicappers are interested in. While it is impressive if teams play and beat good teams to earn a good RPI, it would be far more useful from a betting perspective if those teams were winning their games by 10 points a game than if they were just barely coming out on top.
Another problem is that it measures things that are potentially out of a basketball team’s control. A mid-major will always have a harder time ranking highly than a major conference team – the major conference team plays better teams in conference play, and they are able to schedule more non-conference games against good opponents. Because of that you can find a lot of situations where a very average major conference team has a higher RPI than a very good mid-major team. Because RPI plays a factor in how NCAA teams are seeded in the tournament it is also a reason why there are often upsets of majors by mid-majors – if the RPI were a fairer calculation that more accurately evaluated what a team has to offer then the games wouldn’t have been seen as an upset at all.