The (in)significance of rank in the RPI
In an earlier article, I analyzed the recently proposed changes to the college baseball Ratings Percentage Index (RPI). The RPI's mathematical calculation, which is used to create a number that is calculated to at least four decimal places (e.g. 0.5427), has been well documented. This four decimal number is then used to provide a rank ordering of all teams. Published rankings of the RPI by the NCAA present an interesting but limited view (in that it simultaneously fuels speculation and provides clarity about the worth of one team over another) of how a team will be viewed by an NCAA selection committee.
The ongoing challenge with the RPI in all sports is the perception that it represents a precise measure of one team's quality over another because it is a numeric calculation. This sense of precision is then further reinforced because published RPI listings from the NCAA only provide the rank order of teams, without providing the supporting number that can show incredibly narrow differences (in some cases 1/10,000 of 1 point or less) between teams. The RPI as both a selection tool and information piece for the public could be adjusted in three ways to increase its value.
The ongoing challenge with the RPI in all sports is the perception that it represents a precise measure of one team's quality over another because it is a numeric calculation. This sense of precision is then further reinforced because published RPI listings from the NCAA only provide the rank order of teams, without providing the supporting number that can show incredibly narrow differences (in some cases 1/10,000 of 1 point or less) between teams. The RPI as both a selection tool and information piece for the public could be adjusted in three ways to increase its value.
- All versions (public and private) of the RPI should provide the actual calculated number (to four decimal places) for each team so that the magnitude of difference between two teams can be readily understood;
- Calculation of the RPI should determine if the differences between each team are statistically significant; and
- When the RPI calculation determines that differences between teams are NOT statistically significant, the subsequent rank ordering of teams should list teams these teams as tied in the rankings.
These minor adjustments would clarify public perceptions about the role that RPI plays in at-large selection process for the NCAA Championships. While the RPI is only one tool available for selection, it is a tool that is used repeatedly as a standard measure across which to make comparisons of teams and conferences. These changes would also improve the accuracy of the RPI while providing an on-going reminder that the the RPI is an imperfect tool for selection committees going through their most important duty - determining worthiness of a team to compete for a national championship.
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