I don't Understand RPI

[Spike94]

This has nothing to do with tonights loss by SMC. I just saw the stat on the screen and I really don't understand it. How does SMC have a RPI of 32. I don't see their wins being any better than ours, and their schedule isn't nearly as good as ours. I believe our RPI is in the 60s or 70s and I just don't get it. Does this mean that because our record is worse even though we lost to pretty legit teams our RPI suffered as opposed to winning against lesser teams like SMC? Thanks for the input.

[webspinnre]

Because half of RPI is record, and theirs is better.

[Angelo Roncalli]

From Wikipedia

The current and commonly used formula for determining the RPI of a team at any given time is as follows.
RPI = (WP * 0.25) + (OWP * 0.50) + (OOWP * 0.25)
where WP is Winning Percentage, OWP is Opponents' Winning Percentage and OOWP is Opponents' Opponents' Winning Percentage.
The WP is calculated by taking a team's wins divided by the number of games it has played (i.e. wins plus losses).
For Division 1 NCAA Men's basketball, the WP factor of the RPI was updated in 2004 to account for differences in home, away, and neutral games. A home win now counts as 0.6 win, while a road win counts as 1.4 wins. Inversely, a home loss equals 1.4 losses, while a road loss counts as 0.6 loss. A neutral game counts as 1 win or 1 loss. Note that this location adjustment applies only to the WP factor and not the OWP and OOWP factors. Only games against Division 1 teams are included for all RPI factors. As an example, if a team loses to Duke at home, beats them away, and then loses to Cincinnati away, their record would be 1-2. Considering the weighted aspect of the WP, their winning percentage is 1.4 / (1.4 + 1.4 + 0.6) = 0.4117
The OWP is calculated by taking the average of the WP's for each of the team's opponents with the requirement that all games against the team in question are removed from the calculation. Continuing from the example above, assume Duke has played one other game and lost, while Cincinnati has played two other teams and won. The team in question has played Duke twice and therefore must be counted twice. Thus the OWP of the team is (0/1 + 0/1 + 2/2)/ 3 (number of opponents - Duke, Duke, Cincinnati). OWP = 0.3333
The OOWP is calculated by taking the average of each Opponent's OWP. Note that the team in question is part of the team's OOWP. In fact, the most re-occurring opponent of your opponents is team in question.
Continuing the example above, a team has played Duke twice and Cincinnati once. Duke has played one other game and lost, while Cincinnati has played two other games and won. Next, for simplicity, assume none of the unnamed teams has played any other games.
The OOWP is calculated as (Duke's OWP + Duke's OWP + Cincinnati's OWP ) / 3.
Duke has played and beat the team in question (which, excluding the games against Duke, only lost to Cincinnati), lost to the team in question (excluding Duke, only lost to Cincinnati, and lost one other game (excluding Duke, this team has no WP). Duke's OWP is (0/1 + 0/1) / 2 = 0.0000.
Cincinnati has played the team in question (excluding Cincinnati, they went 1-1 vs. Duke) and won versus two other opponents each of which have no WP when games versus Cincinnati are excluded. Cincinnati's OWP is (1/2) / 1 = 0.5000.
For the team in question, the OOWP is thus (0.0000 + 0.0000 + 0.5000) / 3 = 0.1667
For the team in question, the RPI can now be calculated:
RPI = (WP * 0.25) + (OWP * 0.50) + (OOWP * 0.25)
Plugging in numbers from the above example gives you
RPI = (0.4117 * 0.25) + (0.3333 * 0.50) + (0.1667 * 0.25) = 0.3113

[MDABE80]

Ang...that clears it up for me

[willandi]

Thats really well laid out, but how does the Big East, where several teams are at .500 (at least in conference) rate so high?
I guess the truth is that if we only played OOC games against the expected top teams IN THE MID-MAJOR CONFERENCES, and played them on the road or neutral, we have better RPI (assuming that we win more against the "lessor" opponents.
Seems like a pretty BS thing to skew the balance, but I guess you have to start somewhere.

[Once and Future Zag]

RPI is a very clumsy and imprecise tool as it doesn't take into account the in-game performance, but just captures a "snapshot" when the clock runs out.

Let's say (for simplicity and clarity of explanation sake) CBB played a 5 game season.

Let's say the Little Sisters of the Poor University and Sports Bar plays the following teams

LSOPaSB 64 - Duke 68
LSOPaSB 54 - Ohio State 55
LSOPaSB 103 - Pitt 105 (2ot)
LSOPaSB 85 - Southern - 32
LSOPaSB 90 - Centenary - 54

vs

LSOPaSB 44 - Duke 73
LSOPaSB 54 - Ohio State 93
LSOPaSB 64 - Pitt 82
LSOPaSB 54 - Southern - 51
LSOPaSB 70 - Centenary - 62

In both cases their RPI would be the same - but one is clearly a better team.