In The Slot’s hockey ratings are designed to give an unbiased look at how teams stack up based on game results and the opponents they face. Each ratings system uses different formulas and calculates ratings in different manners:
RPI: The formula used by the NCAA to help selection of teams for all tournament fields. For the purposes of hockey, the basic formula is Winning Percentage (25 percent) + Opponents’ Win Pct. (54 percent) + Opponents’ Opponents’ Win Pct. (21 percent). Note, an adjustment is made to remove a given team’s record from its Opponents’ Winning Percentage.
REC: A team’s overall record. Note: 1.) any games vs. non-MIAA are not included in the RPI calculation; 2.) exclusion games are included in the RPI calculation
SOS: Strength of Schedule, which uses just opponents’ and opponents’ opponents’ record components (ranked 1-198 for each team)
ADJ.SOS: Adjusted strength of schedule; same calculation as SOS, but removing any games in which a team excludes the game
KRACH: A formula touted by many college hockey experts as a better, more mathematically sound alternative to RPI. Ratings are based on an odds scale, so if Team A has a rating of 300 and Team B a rating of 100, Team A would be expected to amass a winning percentage of .750 against Team B if they played enough games.
KRA-tio: A modified version of the KRACH, in which each team receives a percentage of a win or a loss based on a Pythagorean formula. It is designed to reward better defense, so that a 1-0 victory is better than a 4-3 victory is better than a 7-6 victory, even though each are one-goal margins. (For tie games, each team receives 50 percent of a win.)
While RPI is considered “linear” and is calculated in Excel using a relatively simple formula, all other ratings are considered “nonlinear” and must be calculated in Excel using a technique called “iteration.” Essentially, each game result is re-entered into a formula and then ratings are constantly recalculated … as many as 1,000 times for our purposes … until the ratings change on each pass reaches a minimum point and “stabilizes”.