If you're wondering what the RPI ("Ratings Percentage Index") is, or how it's calculated, this post is for you. The RPI has three simple variables: winning percentage (WP), opponents' winning percentage (OWP), and opponents' opponents' winning percentage (OOWP). They are put together in the following formula:
RPI = (0.25 x WP) + (0.5 x OWP) + (0.25 x OOWP)
There's an important home/road complication to the way WP is calculated. For RPI purposes, a home win only counts as 0.6 wins, and a home loss counts as 1.4 losses. Conversely, a road win counts as 1.4 wins, and a road loss only counts as 0.6 losses. So let's say you're 20-10 (actual winning percentage of 67%), and you went 15-4 at home and 5-6 on the road. Your wins, losses, and winning % would be recalculated as follows:
RPI Wins = (0.6 x 15) + (1.4 x 5) = 14.5
RPI Losses = (1.4 x 4) + (0.6 x 6) = 9.2
RPI WP = 14.5 / 23.7 = 62%
The idea here is to recognize the difficulty of winning on the road. A significant effect of this, though, is that you simply reward teams for playing on the road. I don't mind a partial home/road adjustment, but I think the 1.4 and 0.6 factors overestimate the magnitude of home-court advantage. Note: This home/road adjustment does not apply to the calculation of OWP or OOWP.
RPI = (0.25 x WP) + (0.5 x OWP) + (0.25 x OOWP)
There's an important home/road complication to the way WP is calculated. For RPI purposes, a home win only counts as 0.6 wins, and a home loss counts as 1.4 losses. Conversely, a road win counts as 1.4 wins, and a road loss only counts as 0.6 losses. So let's say you're 20-10 (actual winning percentage of 67%), and you went 15-4 at home and 5-6 on the road. Your wins, losses, and winning % would be recalculated as follows:
RPI Wins = (0.6 x 15) + (1.4 x 5) = 14.5
RPI Losses = (1.4 x 4) + (0.6 x 6) = 9.2
RPI WP = 14.5 / 23.7 = 62%
The idea here is to recognize the difficulty of winning on the road. A significant effect of this, though, is that you simply reward teams for playing on the road. I don't mind a partial home/road adjustment, but I think the 1.4 and 0.6 factors overestimate the magnitude of home-court advantage. Note: This home/road adjustment does not apply to the calculation of OWP or OOWP.
There are some additional specifications in terms of how you calculate OWP and OOWP, but the basic idea is straightforward: calculate how your opponents performed (x 0.5), and then calculate how your opponents' opponents performed.
Quiz on Sunday at 6.
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