For those who may not have seen CHODR before, or those who would like another look, here's some explanation of the rating. (This week's ratings were included in a separate post) CHODR - The College Hockey Offensive / Defensive Ratings (pronounced "chowder") 1. What is CHODR? CHODR assigns an Offensive, a Defensive, and an Overall rating to each of the 44 Division I Men's Ice Hockey teams. 2. How are the ratings determined? CHODR places equal emphasis on offense and defense and provides an overall rating for each team based on its offense-defense combination. A team's Offensive rating is based on the goals it has scored, with an adjustment for the quality of the defenses it has faced to score those goals. Similarily, the Defensive rating uses goals allowed and adjusts for the offensive ratings of the opponents. An adjustment is also made for home-ice advantage. The philosophy behind the adjustment calculations is similar to the least squares optimization that was used by Keith Instone's TCHCR. The Overall rating is just the difference between a team's Offensive and Defensive ratings. A more technical explanation of the math is available for those who are interested. 3. How can the ratings be interpreted? (a) An offensive/defensive rating represents the goal scoring/ allowing rate (average goals per game) which would be predicted against a mythical "average" team on neutral ice. An Team with an Offensive Rating of 6 and a Defensive Rating of 2 would therefore be predicted to beat an "average" team on neutral ice by the score of 6 to 2. (b) A positive/negative Overall rating indicates that a team has more/less overall scoring potential than the "average" team. (c) We can rank teams according to their overall ratings or provide separate rankings to reflect offensive or defensive prowess. The better teams have the higher overall ratings, while the better offenses have higher offensive ratings and the better defenses have lower defensive ratings. 4. Comparing individual teams. One nice feature of this system is that it allows comparisons between teams on an easily understood numeric basis. Basically, the difference in overall ratings between two teams represents the predicted average goal differential if they were to play lots of games on neutral ice. Example: Colorado College (2.89 Overall) vs. Boston University (1.89 Overall) would predict an average goal differential of about 2.89 - 1.89 = 1.00 or an even goal in Colorado College's favor. 5. Predicting future scores. Another bonus of CHODR is that it may be used to forecast future scores. The relevant formula is Team A's predicted goals = A's Offensive Rating + B's Defensive Rating - Average Offensive/Defensive Rating +/- Home Ice Advantage Team B's predicted goals = B's Offensive Rating + A's Defensive Rating - Average Offensive/Defensive Rating +/- Home Ice Advantage The Average Rating is subtracted from each team's predicted score because the average is already included in each teams rating, so it ends up getting included twice when the ratings are summed. The Home Ice Advantage value gets added to the home team's predicted score and subtracted from the away team's predicted score. No adjustment is made for a game on neutral ice. The Home Ice Advantage value (currently +/- 0.171 goals) is based on the amount by which home teams hove outscored their oppposition to the current point in the season. EXAMPLE: Let's try BU ( Off = 5.39, Def = 3.50 ) at Maine ( Off = 3.95, Def = 2.49 ): BU's predicted score = ( 5.39 + 2.49 ) - 3.81 - 0.171 = 3.90 Maine's predicted score = ( 3.95 + 3.50 ) - 3.81 + 0.171 = 3.81 Although it may seem awkward to predict non-integral scores, this number actually represents the expected average score for the given team if they played many games under the given conditions (same opponent and same location). Of course, in any one game, the actual result may or may not be close to this average. As we all know, upsets have been known to occur from time to time. 6. Notes: (a) We do NOT use any information about who wins or loses a game in generating the ratings. We are intending only to rate a team's ability to score and keep the other team from scoring. This provides a direct contrast to other ratings which disregared goal differentials. (b) Goals scored in overtime are ignored when generating ratings. We'd also like to eliminate empty net goals, but getting reliable data on those is usually not possible. Thus our ratings reflect the regulation time goal scoring ability. (c) Only games between two Division I teams are counted. No prior information is used in the rating, i.e. all teams are equal at the beginning of the season. (d) Because of the way ratings are calculated, scoring 5 goals against Vermont (Defensive = 2.33) will help your Offensive ratings a lot more than doing the same to Army (Defensive = 5.90). Likewise, allowing 6 goals against Michigan (Offensive = 5.60) won't hurt your Defensive ratings as much as allowing the same number to Mass-Amherst (Offensive = 2.02). This is how the "strength of schedule" figures into the ratings. (e) The estimated ratings are based on a fairly small number of games so far and will tend to exhibit some variability until later in the season. Inter-league play will have a large effect on these ratings as it will in any system which accounts for strength of schedule. Questions, comments, and/or suggestions about CHODR are of course welcomed and encouraged. Timothy J. Danehy Robin Lock [log in to unmask]