by PuckStopsHere on 04/01/12 at 02:24 PM ET
Filip Kuba of the Ottawa Senators is posting a +28 +/- rating so far this season. This is the highest +/- for any player who is not a member of the Boston Bruins. Last season he posted a -26 +/- rating. There were five worse players in the league by raw +/-. Since Kuba played only 64 games in 2010/11, he had the worst +/- on a per game basis in the league. We are seeing a significant improvement in +/- from Filip Kuba. Does this show a considerable improvement in his play?
+/- ratings are significantly influenced by the team for which a player plays. The Ottawa Senators are significantly better this year than they were last year. Last year Ottawa was one of the worst teams in the NHL and had the worst +/- in the East Conference. This year they are a probable playoff team who has scored more goals than they have allowed. A significant portion of Kuba’s +/- improvement is from team improvement.
A problem with +/- is that is only records an event when a goal is scored. Some goals are bad goals and some scoring chances that do not result in goals are better chances. Shots based analysis is better than +/- based because it contains more events and hence better statistics and does not include the randomness of when goals are scored. One measure of how lucky a player is regarding the goals scored when he is on the ice is PDO. This is the shooting percentage of all teammates when a player is on the ice plus the saves percentage of his goalie at even strength. This number will be 1000 on average for all players. Those players significantly above 1000 are playing in an unsustainably good situation and those well below 1000 are having unsustainably bad luck. Kuba had a 949 PDO in 2010/11, which was the worst of any player who played more than sixty games in the league. He had unsustainably bad luck. Given time things would get better. They did. This season his 1032 PDO is a team best. The team situation and random chance explain a large part of Kuba’s +/- improvement.
Filip Kuba’s +/- improvement shows that +/- (goals based) analysis can be flawed. It is strongly influenced by shooting and saves percentages which are usually unsustainable. If we turn to shots based (Corsi) analysis we see less of a swing from season-to-season of Kuba’s numbers. We see that his level of play is better captured by Corsi-type numbers.
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