A Primer on Varoius Rankings Methods

Author’s Note:  This is another piece I’m moving over from elsewhere.  I cut down a lot of the dated info to just the bare-bones description of various rankings systems.

For those of you that are familiar with advanced stats, this will be old hat, but for those that aren’t, one of the best ways to track the general skill of a team is through shot attempts (shots on goal + missed shots + shots taken that get blocked) versus the opponents’ shot attempts.  Generally the team that takes more shots is controlling more of the play and is better at hockey.  It’s not an exact science, and it may be less useful at the NCAA level where there is a wider gap between the best and worst players (and teams), but it’s a fairly accurate predictive stat.

Unfortunately, so far as I can tell, only shots on goal are recorded in Women’s hockey so that limits things a bit, but they can still be used to get a general idea of who’s controlling play and by how much.  I called this stat Shots Percentage, or S%.

Of course NCAA hockey teams only play a handful of teams outside their conference, so one team’s S% is not necessarily usefully compared to another’s.  I sought to correct this by determining the quality of their opponents (Opponents Shots Allowed Percentage or Opp SA%) and taking the difference between the two numbers, with positive numbers being good (a team performed better than average vs. their opponents) and negative numbers being bad.  To give an example:

Quinnipiac outshoots their opponents 40-10 every game.  Their S% is therefore 80% (40 shots taken divided by 50 total shots).  This seems like a good thing, but when we look at Quinnipiac’s opponents we find that they were outshot 40-10 every single game.  So their OPP SA% is 1 minus (10 divided by 50) or also 80%.  Quinnipiac’s 40-10 performance isn’t exemplary considering the quality of their opponents (everyone outshoots them 40-10), it’s merely average so their Relative Shots Percentage (Rel S%) is 80%-80% or 0%.

To see how teams fared against the best opponents, I did the same calculation for every team only considering opponents that had a positive shot differential or a S% above 50%.

Womens Hockey Stats

Rel S% is in yellow because that’s what I chose to sort by.  The top 10 teams in each category are in green and the bottom 10 are in red.  When I compile my weekly rankings I sum each team’s ranking in the following categories:

  • Overall winning percentage (pct)
  • Percentage of shots taken (S%) – (Editor’s Note – This is essentially the best imitator of Corsi %.  I’m told that shot attempts (Shots on goal plus missed shots plus shots taken that get blocked) are recorded but that data is not available anywhere.) 
  • Percentage of shots taken relative to Opponents’ S% (Rel S%)
  • S% versus teams with an S% of 50% or more
  • Rel S% versus teams with an S% of 50 or more
  • Shooting Percentage (Sht%)
  • Save Percentage (Sv%)

USCHO Poll:

The USCHO Poll is exactly what it sounds like, the USCHO writers vote, those votes are summed, and the teams are ranked accordingly.

The Pairwise Rankings:

“…compares teams with an RPI over .500 (Teams Under Consideration or TUC per the NCAA Women’s Division I ice hockey championship manual), judging them by these criteria: record against common opponents, record against teams under consideration, head to head competition, and the Ratings Percentage Index (RPI).

For each comparison won, a team receives one point. The final PWR ranking is based on the number of points (comparisons) won against teams under consideration. Ties are settled by the RPI.”

RPI Rankings:

The Ratings Percentage Index is one tool used to select teams for the national collegiate ice hockey tournament. Only results from games between Division I and II teams are used. Factors involved are 1) the team’s winning percentage; 2) the average winning percentage of the team’s opponents; and 3) the average winning percentage of the team’s opponents’ opponents. These factors are multiplied by 30%, 24%, and 46% respectively.

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About Alex

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