While this method removes many of the biases from raw plus-minus, it is still an imperfect method of rating players. First, most importantly, it is for even-strength play only. Second, a player’s linemates or defence partner may exert a major influence on a player’s numbers – see Milan Hedjuk for a prime example. Third, the on-ice/off-ice method of adjusting for team implicitly compares a player to the other players on his team who play the same position but on another line or D-pairing. If a player is on the same team as a great player, the off-ice baseline may not be a fair comparison. For example, Ted Green’s 1971 season has one of the lowest adjusted plus-minus ratings ever. When you realize that much of his off-ice baseline was set by Bobby Orr, the reason for the low rating becomes clear. Also, some players play more difficult opposition than others, facing the other team’s best players and taking more defensive zone faceoffs. These differences can also skew the numbers.
For the above reasons, please keep the following in mind when using these numbers to evaluate players
- Adjusted plus-minus is best used to compare players who played in a similar role. For example, compare #1 defensemen who played the toughest ice-time on the team to other #1 defensemen, not to #6 defensemen who were sheltered by their coaches from the best players. For example, take Tom Preissing’s rating with a huge grain of salt.
- Adjusted plus-minus is measured against a baseline of average, so it will tend to underrate players with a long decline phase or several poor years at the start of their career (Mark Messier) and give high ratings to players who retired young and didn’t play a lot past their prime(Bobby Orr, Eric Lindros).
- Adjusted plus-minus is measured against a baseline of average, so it will tend to underrate players with a long decline phase or several poor years at the start of their career (Mark Messier) and give high ratings to players who retired young and didn’t play a lot past their prime(Bobby Orr, Eric Lindros).
- Check to see who the player’s linemates were. Did he have a great player on his line? Charlie Simmer and Dave Taylor both have very high ratings, and likely owe much of it to Marcel Dionne.
- Did the player play on a team with another great player who was on another line/D-pairing? If so, his adjusted plus-minus may be too low. Mark Messier in his Edmonton years is an example here, along with Ted Green. I don’t think there are too many cases of this kind, but there are certainly a few.
- There may be a significant amount of random variation in a single-year result. For that reason, I would look at multiple years when measuring a player’s peak, and would not use this stat as definite proof that one player was better than another in a given year.
There are a lot of disclaimers there, but I still believe there is a lot of good information in adjusted plus-minus when evaluating a player’s career. Even after taking the above possible biases into account, there are still some very interesting results.