The Ratings Percentage Index, more commonly referred to as the RPI, has its flaws, but is not yet in its final days. The demise of the RPI was over-exaggerated, and it is still used for postseason selection despite the known struggles with the metric.
The RPI is another way to dive deeper into a team’s record. Some records do not tell the whole truth of how the team plays or who a team has played against. For that reason, RPI was created in 1981 to show a team’s strength of schedule and its’ opponents strength of schedule.
The RPI does a couple things right. It weighs matches against teams with better win percentages higher than those against weaker teams. 50% of the RPI formula is based on the opponent’s winning percentage, which means that playing teams with better records gives a larger RPI boost.
The other half of the formula revolves around other winning percentages.
The RPI formula is 0.25 (team’s winning percentage) + 0.5 (opponent winning percentage) + 0.25 (opponent’s opponent winning percentage).
The formula appears to be simple, which hurts the RPI’s effectiveness. Not every formula is perfect, but the RPI has come under more scrutiny than most throughout the years for various reasons.
Road and home wins have the same value in the RPI, but a road win carries more significance than a home win in actuality. In volleyball, Wisconsin’s sweep of Nebraska on the road is much more impressive than the Badgers’ sweep of No. 6 Penn State three days earlier at home.
Road wins matter and though Wisconsin will still get a boost from the eye test, measuring their value is just as important. The losses are more important, yet they are just thrown in as part of the winning percentage.
The RPI formula puts so much emphasis on strength of schedule that a team’s wins and losses can be lost in the mix. One way losses affect the RPI is that when conference play begins, better conferences help every team out.
An opponent’s win percentage is half the RPI formula and another quarter is the opponents’ winning percentage. A conference with great teams at the top also helps the middle and lower teams. Power five conferences tend to have the stronger teams, and those conferences are perceived as the best in the RPI.
Losses are another part of the RPI formula cause criticism. To some, losses in stronger conferences do not affect teams as much. Another issue is how not only road and home wins are weighed, but also home and road losses. The RPI only captures the teams in the schedule and their overall record — not other factors in the wins such as venue and time.
The NCAA began to adapt this idea by putting it into the NET rankings, but those rankings are only for men’s basketball right now. The way forward is to form a formula specific to each sport instead of one formula that is supposed to work well for every sport.
Only one NCAA sport has officially stopped using the RPI metric — men’s basketball last season. Almost every other college sport still uses RPI in its NCAA Tournament selection process for at-large teams.
The problem is that instead of the NCAA Tournament being hosted at neutral sites, some sports have the higher seed host the postseason matches. None have as big of an advantage as college volleyball where the top seeds have home court advantage and a one-seed plays at home until the Final Four.
That massive advantage puts even more weight on the committee’s selection and RPI is still one of the final determining factors in seeding.
The usage of RPI has mostly correlated to the top four seeds in each region. In 2018, 15 of the top 16 RPI teams were at least a four seed within their respective region. The difference was where they were seeded.
Nebraska was the seventh overall seed despite being ranked 11th in the RPI and faced 15th overall seed Oregon, who was 19th in RPI, in the regional finals.
For Nebraska, the RPI helps more than it hurts. The Big Ten is the No. 2 conference in RPI for volleyball, which significantly helps Nebraska’s chances if it were to drop more games. Stronger conferences get more benefits, as seen in last year’s regional match, but the RPI is on its way out.
The next stop for tournament selection is whether each sport creates its own formula or if they will continue using the one-size-fits-all metric.