by PuckStopsHere on 09/10/12 at 05:11 PM ET
Yesterday I wrote about using Fenwick rankings when the score is close to rank how good a team is. I want to compare this with a simpler team Corsi ranking. These are attempts to measure and quantify puck possession and use it to infer the ability of hockey team. To begin this study I want to present the raw data. Fenwick data is usually reported as a percentage of events (shots on goal and missed shots) that a team is responsible for. Corsi is usually listed as a +/- number (Corsi events for minus those against), thus we will be more concerned with relative rankings than with raw numbers.
Here are Fenwick close score rankings for teams compare with team Corsi rankings:
|Team||Fenwick Rank||Close Score Fenwick||Corsi Rank||Team Corsi|
|St Louis Blues||1||55.07%||9||+264|
|Detroit Red Wings||3||54.39%||1||+648|
|Los Angeles Kings||4||53.60%||3||+636|
|San Jose Sharks||7||52.19%||8||+313|
|New Jersey Devils||10||51.08%||13||-23|
|New York Rangers||14||49.90%||25||-334|
|New York Islanders||18||49.18%||26||-351|
|Tampa Bay Lightning||20||48.31%||29||-391|
|Columbus Blue Jackets||25||47.53%||24||-306|
|Toronto Maple Leafs||28||46.70%||18||-163|
For the most part it is clear from looking at this chart we are measuring essentially the same number. The teams that do well by Fenwick close also do well by Team Corsi and vice versa. There are a few teams that have some difference between their ranking in both systems. These include the Fenwick leading St Louis Blues, the New York Rangers and Islanders, Toronto Maple Leafs and Nashville Predators. I think most of the remaining discrepancy is essentially meaningless error from the differences between the two systems. The difference in the rankings is minimal in these cases. Hence we learn something by looking at the five cases I have found as being most different.
The causes for discrepancy include the frequency and style of play of teams when a score is not close. Some teams are more competitive in games that are no longer close than others and some teams get into blow-out situations more often than others. There is also discrepancy due to shots blocked. Corsi includes these and Fenwick does not. This can have an effect in teams that block a lot of shots. I think a couple case studies in these teams with larger discrepancies between the two systems will be informative and I will do them in the future.
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