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  1. #1

    KenPom versus the RPI

    It's become fashionable to bash RPI and praise Ken Pom. And for illumination, I admire Ken Pom's tempo-based formulas.

    But are Pomeroy's rankings better than the RPI rankings? Really?

    Compare the two rankings with the two voter polls, which right or wrong, seem to offer the best guage for the top 10 teams.

    The RPI top 10 is (with AP/coaches rankings):

    1. Syracuse (2/2)
    2. Duke (5-4)
    3. Kentucky (1/1)
    4. Michigan State (7/8)
    5. UNC (8/7)
    6. Baylor 9/10
    7. Kansas (4/5)
    8. Ohio State (6/6)
    9. Missouri (3/3)
    10. Southern Miss (unr/unr)

    Georgetown (10/9) is the only top 20 team that misses the list ... hey are 13 in the RPI. The only real outlier in the RPI top 10 is No. 10 Southern Miss. That's not outrageous -- they are 22-4 an tied with Memphis for the lead in Conference USA.

    Compare that with Ken Pom's top 10:
    1. Kentucky (1/1)
    2. Ohio State (6/6)
    3. Michigan State (7/8)
    4. Kansas (4/5)
    5. Syracuse (2/2)
    6. Wisconsin (unr/unr)
    7. North Carolina (8/7)
    8. Missouri (3/3)
    9. Wichita State (unr/unr)
    10. St. Louis (unr/unr)

    New Mexixo (unranked/unranked) is No. 11. Duke (4/5) is No. 14 and Baylor (9/10) is No. 15.

    His list looks okay in the top five (as does the RPI), but his second five is out there. Pomeroy wrote a blog entry last month just shrugging his shoulders over the bizarre high ranking for a so-so Wisconson, essentially admitting that it's a glitch in the system. Wichita State, St. Louis and New Mexico are (like Southern Miss) strong mid-majors, but nobody in either poll has any of them in the top 25 ... much less top 10.

    I'm not suggesting that Pomeroy's rankings are without value or that the RPI is this great predictor. Or even a better predictor. I just think it's suddenly become fahionable in journalistic circles to trash the RPI ... and to laud Pomeroy -- as Eamonn Brennan of ESPN did on twitter last night. But as Brennan admitted after an e-mail exchange with an NCA official, he uses the RPI in his bubble report.

    I guess the point of my post is not to get carried away with any predictive poll .. either good or bad. RPI is a big deal because the committee relies on it heavily -- not in the sense that they say, oh, N.C. State is 49 and Murray State is 50, therefore NC State should get the last at-large spot. What they do use it for is to look and say, well, NC State has four top 100 wins and Murray State just has three top 100 wins. They look at top 50 wins ... road wins ... non-top 100 losses -- all based on the RPI.

    In the past, the human polls -- AP and the coaches -- have been better predictors of the top seeds than either RPI or Pomeroy. Both of the computer poll (along with Sagarin) are useful to a degree.

  2. #2
    Join Date
    Feb 2007
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    Washington DC
    I think Kedsy or someone demonstrated how a team could game the RPI by playing a ton of tough teams to pad their strength of schedule and winning none of them.

    I'd say KenPom can tell you a lot more about a team than RPI because it uses more data to make its rankings and produces a clear picture of the team. But that's not to say the rankings are better or worse, just that it tells you more.

    Another issue is in college basketball anyone can beat anyone, so neither is a great predictor of future tournament success. They can both tell you where you've been and what you might see, but as Butler and others prove every year, anyone can get hot.

  3. #3
    Join Date
    Dec 2010
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    The Republic of Texas
    I'm curious as to the RPI and KenPom rankings from the last 3 seasons of Final Four teams and National Champions of that season going into the NCAA Tourney. Anyone have this data?

  4. #4
    Join Date
    Feb 2007
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    Norfolk, VA
    Quote Originally Posted by Chris Randolph View Post
    Anyone have this data?
    Google.
    Bob Green

  5. #5
    Quote Originally Posted by Olympic Fan View Post
    It's become fashionable to bash RPI ... I just think it's suddenly become fahionable in journalistic circles to trash the RPI ... ...
    Scott Van Pelt had a long-ish anti-RPI rant on his radio show this week.

  6. #6

    Here's Sagarin

    1 Kentucky
    2 Ohio State
    3 Syracuse
    4 Kansas
    5 Michigan State
    6 Missouri
    7 North Carolina
    8 Wisconsin
    9 Indiana
    10 Duke

  7. #7

    Here's sports-reference

    1 Kentucky
    2 Ohio State
    3 Kansas
    4 Michigan State
    5 Syracuse
    6 North Carolina
    7 Duke
    8 Indiana
    9 Wisconsin
    10 Wichita State

  8. #8

    Duke is # ...

    2 - RPI
    4 - coaches
    5 - AP
    7 - sports-reference
    10 - Sagarin
    14 - Kenpom

  9. #9
    I think you're missing part of the point. The RPI may resemble our intuition of what teams are good better, and it may even actually resemble the reality of what teams are better - but it's still arbitrary. Here's my theoretical ranking system: take the AP poll every week, switch the #8 and #13 teams around, and replace #24 with Wake Forest. Such a ranking system would probably give overall better predictive value than either the RPI or kenpom... but that doesn't mean it makes sense.

    The RPI is a fundamentally arbitrary system. Why does your record count for 25% instead of 20% or 30%? Kenpom isn't perfect, but all the factors have some sort of basketball or mathematical justification to them. That's the point. Even if the predictive power isn't perfect - or even if it happens to be worse than the RPI - it's still a tool that makes sense.

  10. #10
    Join Date
    Nov 2007
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    Delaware
    This is one area where I really agree with Jay Bilas, who while preferring tempo-free and margin based metrics over pure win/loss metrics, also acknowledges that no one formula can be perfect. I think that a greater sample size is necessary to remove biases in individual formulas. You can pick through any formula and find things that are just plain wrong. I know that Colorado State is a top 30 team in the RPI, which is pretty bad. Worse still is KenPom having St. Louis at 10. He'd probably be the first to admit that.

    I'd like to see the RPI replaced with a consensus rating system that combines ratings like the RPI, Sagarin, Pomeroy, Massey, LMRC, and the new ESPN computer rankings. I'd like a mix of win/loss based systems and margin based systems because each of them tend to ignore the value of the other. There's a much bigger difference between a 1 point loss and a 1 point win than margin based systems will tell you, but there's also a difference between a 1 point win and a 20 point win which win/loss systems ignore completely. We could easily combine these ratings by dropping the outliers for each team and averaging the rest. We could call it the Basketball Consensus Standings, or BC- oh wait...that acronym has already been taken. Seriously, though, I think basketball can find some value in the way that the BCS compiles its computer data in football. The problem with the way football uses it is that they take those numbers pretty much as is, with 1 being better than 2, 2 being better than 3, etc. If basketball could take the objective consensus data, but apply it in a subjective way (just like the committee does with the RPI right now), we'd have a much better system with less to complain about.

    The NCAA already gives all of this information to the committee, but still uses the RPI as the basis of their data sheets. If they could just switch that data with less biased consensus data, the committee would have a much clearer picture. While I'm on the subject, I would be remiss not to include one valid concern that the NCAA would have with incorporating margin based systems, and that is putting incentive on running up the score to improve computer numbers. This was a very big concern for the BCS and for years, when the computers decided most of the rankings and the polls were just a small part, coaches and conferences were concerned that teams would just bury other teams for four quarters when it wasn't necessary to improve computer ratings. Contenders were worried about players getting hurt and non-contenders were worried about embarrassment. At first the computer ratings were prevented from using margin of victory, but that restriction has since been lifted without much detriment to the game. It's certainly a concern that the NCAA should have, but I don't think it should be big enough to prevent a move. If enough win/loss systems are included to balance out the ratings, and the ratings are only used indirectly, I can't possibly see it being too big of a detriment.

  11. #11

    St. Louis

    Why is Kenpom having St. Louis at 10 so crazy? Sagarin has them at 15. Sports-reference has them at 20.

    There are 344 teams. These computers are good at placing teams in broad swaths correctly.
    Kenpom ranks 2.9% teams higher than St. Louis ... Sagarin says no, 4.3% are ranked higher ... Sports-ref 5.8% ... no matter what, St. Louis is good (per the computers) ... 97th percentile ... 95th percentile ... 94th percentile ...

  12. #12
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    Quote Originally Posted by Reilly View Post
    Why is Kenpom having St. Louis at 10 so crazy? Sagarin has them at 15. Sports-reference has them at 20.

    There are 344 teams. These computers are good at placing teams in broad swaths correctly.
    Kenpom ranks 2.9% teams higher than St. Louis ... Sagarin says no, 4.3% are ranked higher ... Sports-ref 5.8% ... no matter what, St. Louis is good (per the computers) ... 97th percentile ... 95th percentile ... 94th percentile ...
    There's no way that St. Louis is anywhere near a top 10 team. The margin based computers give them way too much credit for beating up on bad competition. I'm not saying that St. Louis is bad, but they have a pretty poor SOS, their best win is a pretty good win at Xavier, but their next best win is probably either Washington or Dayton. They don't have any terrible losses, with @LMU and @UMass being the worst, but I'd think you'd be hard pressed to call it a top 10 resume. The win/loss systems (RPI, Sagarin's ELO Chess) have them more in the 20's or 30's. The point wasn't just to pick out examples, but to kind of show that their are outliers in every system because of the individual biases of each that can be removed by considering them all on a consensus basis.

  13. #13
    The sports-reference SRS says it is based on points *and* strength of schedule. So, not a points-only basis. It has St. Louis at #20. The distance from #10 to #20 is not that much of an outlier. One is 97th percentile and one is 95th percentile. I'm prone to agree w/ you that a consensus may take off the rough edges; but I don't see St. Louis at 10 as that much of an outlier, when others have them at 15 and at 20.

  14. #14
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    Delaware
    Quote Originally Posted by Reilly View Post
    The sports-reference SRS says it is based on points *and* strength of schedule. So, not a points-only basis. It has St. Louis at #20. The distance from #10 to #20 is not that much of an outlier. One is 97th percentile and one is 95th percentile. I'm prone to agree w/ you that a consensus may take off the rough edges; but I don't see St. Louis at 10 as that much of an outlier, when others have them at 15 and at 20.
    I'm not looking to make a big deal about St. Louis. I was just scrolling for the first example that felt wrong to list. After looking at all the ratings, St. Louis at 10 probably isn't an outlier among computers, but it still doesn't mean that St. Louis is in the top 10 teams. There are plenty of computers that fall all over the spectrum from pure win/loss, to hybrid, to pure margin based. I don't know much about the SRS, but using SOS is very different from using win/loss. KenPom uses SOS as well. It's just a way to adjust the margin for the strength of your opponent, but it doesn't create a wide gap between a win and a loss in the same way as a non-margin system does. Other computers might have them rated high, in fact, the BPI thing that ESPN just came out with has them at 9, but that still doesn't feel right to me. This is why you still apply the computers subjectively with the committee. Even if St. Louis computer average came out somewhere in the teens or low 20's, they probably shouldn't be a 5 or 6 seed. Lunardi has them at 9 right now (around low 30's on the S-curve) which feels right. Even a consensus computer won't get every team right, but it will probably be closer to an accurate measure than any individual poll. I'd love to have a discussion on the merits of computer rating systems here, but we should probably take the individual team talk over to a bracketology thread. I'd certainly like to have that discussion, but we're getting close to hijacking a thread about a different topic.

  15. #15
    Quote Originally Posted by Chris Randolph View Post
    I'm curious as to the RPI and KenPom rankings from the last 3 seasons of Final Four teams and National Champions of that season going into the NCAA Tourney. Anyone have this data?
    I don't have all the data, but I seem to recall that going into the tournament in 2010, KenPom's numbers predicted we would win. I can honestly say I was not so confident.

  16. #16
    Quote Originally Posted by SCMatt33 View Post
    [1] I'm not looking to make a big deal about St. Louis. I was just scrolling for the first example that felt wrong to list. ... Even if St. Louis computer average came out somewhere in the teens or low 20's, they probably shouldn't be a 5 or 6 seed. ... Even a consensus computer won't get every team right, but it will probably be closer to an accurate measure than any individual poll. ... we're getting close to hijacking a thread about a different topic.
    I don't believe we're close to hijacking a thread at all. We're using St. Louis as an example of how different polls treat different teams, and if one peels that treatment back, it gets at what those ratings systems may be valuing.

    Just as we'll use Duke as an example, and many other teams as an example, as the thread continues. The OP started with exactly that sort of feeling: "look at what this poll has -- that seems whack ..."

    A theoretical computer poll discussion that mentions *zero* teams? I guess such a thing is possible, but doubt it has ever happened. I suppose it would entail a discussion of things that one believes go into making a good basketball team (and what's the definition of "good") and what should be valued: wins, points, certain efficiencies, how to measure those things, what proportions to weigh the different numbers.

    On the St. Louis example, I'm not seeing much for or against them. You argue that it *feels* wrong. On some level, the computers are supposed to get past such feelings. I don't know much of anything about St. Louis - other than Majerus is their coach, and Spoonhour died here recently. I certainly don't know their players or pace or strong suits or weaknesses. I do know a computer valuing certain things thinks they are 10, another 15, another 20 ... out of 344. So, they are doing the things that those who think about these things (and who set up the computers) value.

    I don't know what you value: why does St. Louis not "feel" right? Why a 9 seed and not a 6 or a 5 seed? I don't know what I value, either, necessarily. I also don't know the underlying math and equations for any of these rating systems. I -- like you -- judge on feel. I follow college football pretty closely, and SRS at the sports-reference CFB site usually feels pretty accurate to me. I'm coming at this via back-tracking and feeling: look at a system, then, does it jive overall with what all I know? If yes, then it's a good system! Sort of how those who agree with me, or find me funny or smart or to be a stand up guy, seem to have exceptional taste in humans ...

  17. #17
    Quote Originally Posted by Chris Randolph View Post
    I'm curious as to the RPI and KenPom rankings from the last 3 seasons of Final Four teams and National Champions of that season going into the NCAA Tourney. Anyone have this data?
    I don't know that this would prove much. (I also don't know that you were even insinuating that it would prove anything; it would be neat to look at such numbers.) Wasn't VCU #85 in maybe the RPI or Kenpom? That doesn't prove that that particular ststem is right, or wrong, or that that system is better, or worse, than some other system that had VCU higher, or lower. All it proves is that a team that that ststem -- valuing what it values -- ranks at #85 can get to the Final Four, or, has gotten to the Final Four.

    In other words, a team that a system values as being in the top 25% (85/344) of all of college basketball can knock off 4 other teams also valued in the top 25% of all of college basketball. Which doesn't tell us much at the end of the day.

    At Duke, I had a literature class with a future Rhodes Scholar. My insights were consistently better than his; at one point, he even mentioned not understanding a certain text at all, while the professor kept going back to my input to explain it to everyone. He had a higher RPI than me, but I was good enough to be in the game, and had a nice run.

  18. #18
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    Arlington, VA
    Quote Originally Posted by Olympic Fan View Post
    It's become fashionable to bash RPI and praise Ken Pom. And for illumination, I admire Ken Pom's tempo-based formulas.

    But are Pomeroy's rankings better than the RPI rankings? Really?

    Compare the two rankings with the two voter polls, which right or wrong, seem to offer the best guage for the top 10 teams.

    The RPI top 10 is (with AP/coaches rankings):

    1. Syracuse (2/2)
    2. Duke (5-4)
    3. Kentucky (1/1)
    4. Michigan State (7/8)
    5. UNC (8/7)
    6. Baylor 9/10
    7. Kansas (4/5)
    8. Ohio State (6/6)
    9. Missouri (3/3)
    10. Southern Miss (unr/unr)

    Georgetown (10/9) is the only top 20 team that misses the list ... hey are 13 in the RPI. The only real outlier in the RPI top 10 is No. 10 Southern Miss. That's not outrageous -- they are 22-4 an tied with Memphis for the lead in Conference USA.

    Compare that with Ken Pom's top 10:
    1. Kentucky (1/1)
    2. Ohio State (6/6)
    3. Michigan State (7/8)
    4. Kansas (4/5)
    5. Syracuse (2/2)
    6. Wisconsin (unr/unr)
    7. North Carolina (8/7)
    8. Missouri (3/3)
    9. Wichita State (unr/unr)
    10. St. Louis (unr/unr)

    New Mexixo (unranked/unranked) is No. 11. Duke (4/5) is No. 14 and Baylor (9/10) is No. 15.

    His list looks okay in the top five (as does the RPI), but his second five is out there. Pomeroy wrote a blog entry last month just shrugging his shoulders over the bizarre high ranking for a so-so Wisconson, essentially admitting that it's a glitch in the system. Wichita State, St. Louis and New Mexico are (like Southern Miss) strong mid-majors, but nobody in either poll has any of them in the top 25 ... much less top 10.
    Small technical correction (hope I'm not repeating something already said; didn't see it in a quick skim of the thread)--Wichita State is actually ranked 24th in the AP poll; they are the unofficial "26th" team in the coaches' poll.

  19. #19
    Quote Originally Posted by Chris Randolph View Post
    I'm curious as to the RPI and KenPom rankings from the last 3 seasons of Final Four teams and National Champions of that season going into the NCAA Tourney. Anyone have this data?
    I have this data, but can't give it to you until Monday. And you probably can't google it, because you'd get post-tourney data.

  20. #20
    Quote Originally Posted by SCMatt33 View Post
    There's no way that St. Louis is anywhere near a top 10 team. The margin based computers give them way too much credit for beating up on bad competition. I'm not saying that St. Louis is bad, but they have a pretty poor SOS, their best win is a pretty good win at Xavier, but their next best win is probably either Washington or Dayton. They don't have any terrible losses, with @LMU and @UMass being the worst, but I'd think you'd be hard pressed to call it a top 10 resume. The win/loss systems (RPI, Sagarin's ELO Chess) have them more in the 20's or 30's. The point wasn't just to pick out examples, but to kind of show that their are outliers in every system because of the individual biases of each that can be removed by considering them all on a consensus basis.
    I'd argue this. They also lost to a Really good New Mexico team on the road only by 4 (a close game all the way appaerntly) and the A10 is a far better conference than people give credit this year...and St. Louis has mainly ripped through it. The only truly bad teams (think Wake or BC) in the conference are Fordham and Rhode Island, and St Louis hasn't played either team yet.

    La Salle and St. Joes on the road are tough opponents, yet St. Louis just beat both and neither game was close...and they only have one truly bad loss, to UMass.

    Do I think they're better than Duke? Maybe not, but I think it's certainly close and I'd be really worried if we were to face them.

    EDIT: Put it this way: If they were named "Temple" instead of St. Louis, I think they'd get a lot more credibility.
    <devildeac> anyone playing drinking games by now?
    7:49:36<Wander> drink every qb run?
    7:49:38<loran16> umm, drink every time asack rushes?
    7:49:38<wolfybeard> @devildeac: drink when Asack runs a keeper
    7:49:39 PM<CB&B> any time zack runs, drink

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