Re: NCAA Basketball Drops RPI for Tournament Selection
http://www.espn.com/mens-college-ba...4445390/ncaa-announces-new-ranking-system-rpi
I have no idea what the math of the new system looks like, though the NCAA's history doesn't make me very confident that it will be very good. Still, will be interesting to see whether this is a start of moving on from an RPI based system (which PWR is) in all sports.
The short explanation (maybe too short) of the rankings they are going to use - Ken Pomeroy - is a calculation of offensive and defensive efficiency.
A Basketball game is a series of alternating ball possessions; team A has the ball, then team B gets the ball, then team A, etc etc. In an average game, each team might get 70 possessions over the course of the game. If team A averages one point per possession, and team B averages only 0.9 points per possession, team A wins 70-63.
Some teams like to play 'fastbreak' basketball, that over the course of a season might end up raising their possessions per game to 80 or 90 or 100. Other teams like to play slow, deliberate 'half court' offense that gets them to 50 possessions per game. If each averages one point per possession, the fastbreak team is averaging 90 points a game, while the slow team is averaging only 50 points a game.
But what if the slow 'half court team' is more efficient, averaging 1.1 points per possession, 55 points a game. And what if the fast team played the slower team? At a glance, one team is averaging 90 points a game, and the other only 55 points a game. Fast team is gonna win, no?
No, probably not. Because the game is going to be maybe a 70 possession game, faster than 'slow' would like, but slower than 'fast' would like. And assuming their point per possession efficiency stays the same, slow is going to score 77 with their 70 possessions, while fast is only going to score 70.
Same idea for defense: points per possession given up.
The Pomeroy ranking 'normalizes' each team's offensive and defensive 'per possession' efficiency, and then uses those numbers in a predictive calculation to rank the teams overall.
There are a bunch of other 'fudge factors, including home/away/neutral site, conference, others I forget. But the basic idea is this per possession efficiency.
I can't imagine that it would be applicable to hockey in any usable way.