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B1G Hockey: What are KRACH and PairWise?

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A primer on KRACH ratings and why I use them.

Bruce Bennett/Getty Images

I gave a brief intro on KRACH in one of my first FanPosts so I thought I would repost for those of you who missed it.

KRACH

I will be using KRACH ratings to project future results.  Go read that FAQ.  Now. It is great and explains why College Hockey News (and I) prefers KRACH to the NCAA's RPI.  Here is another great resource.  Scroll down past the table to see mathematical explanations and comparisons to RPI.

KRACH utilizes Bradley-Terry ratings to figure out how teams compare. Bradley-Terry ratings utilize logistic regression to compare all teams based solely on results of games played.  I know that KRACH ratings are not meant to be used to predict future results and only say anything about past results, but I think they can give some insight into how the conference race may play out.

KRACH expected win% example:

  • Team A Rating: 150
  • Team B Rating: 50

Team A expected win % = 150/(150+50) = .750
If Team A and Team B were to play enough times, Team A would be expected to win 75% of the time. If you took a teams expected win percentage against the schedule played, it should equal the teams actual overall record.  These rankings are effective only once there is enough "connected-ness" between all teams in D-1. This usually happens in the beginning to middle of December.  Unfortuantely, college football doesn't have enough cross-over between conferences for this to be a useful ranking method.

To project a teams' expected points I take the current number of points and add the Projected points against each team left (3*number of games against opponent*expected win% against opponent for each opponent left on the schedule). KRACH ratings are updated on collegehockeynews.com and uscho.com on a nightly basis.

PairWise

There are 59 teams in college hockey. The pairwise is an approximation of the selection process for the NCAA tournament. Again, College Hockey News does a great job explaining the process.  The top 16 teams are selected for the tourney. Conference tournament champions get auto-bids so teams rated near 16 can be displaced if a lower ranked team wins it's conference tournament.

Teams are compared pairwise against every other team in the country.  The comparison criteria are RPI, common opponents, and head to head.  If teams tie in a comparison, the team with the higher RPI has genereally wins the overall comparison but it is not an official rule.

Please read those FAQs before asking further questions as they likely have your answer.