Advanced Hockey Statistics
"What questions does it answer?"
There are a number of new statistics that have been developed in the 21st century (i.e. since about 2007) that have helped analysts and fans to better understand the game. What follows is a brief overview of these statistics.
Corsi and Fenwick
Corsi and Fenwick are similar to the traditional +/- stat, but instead of goals it is based on shots. They attempt to answer the question, "Who is controlling possession of the puck?". Because there aren't possession stats in hockey (yet?) we instead use shots as a proxy, which has been shown to correlate well with puck possession. This can be presented as a +/- stat (i.e. total shots for - total shots against) or as a percentage (i.e. total shots for / (total shots for + total shots against)).
Corsi For (CF) = Shots + Misses + Blocks Against
Corsi Against (CA) = Shots Against + Misses Against + Blocks For
Corsi For % (CF%) = CF / (CF + CA)
Corsi = CF - CA
Fenwick is essentially the same as Corsi, but it excludes blocked shots.
Expected GF/GA and +/-
While Corsi and Fenwick count shot attempts, they don't account for quality of the shot. Expected +/- considers the shot location, and uses league-wide averages to determine the likelihood of that shot being a goal. It doesn't factor in whether the shot actually resulted in a goal or not. Instead, it's giving a sense of shot quality by looking at the odds of scoring a goal from that location.
A team which has an Actual Goal Differential exceeding its Expected Goal Differential ('axDiff') indicates a team converting or stopping an inordinate amount of good chances compared to league average. This could indicate the team has great shooters, a prolific goalie, or is just getting lucky.
A negative differential would indicate a team is getting more good chances than its opponent, but is not converting or is allowing more than league norms. This could mean bad shooting, bad goaltending, or just being unlucky.
Scoring Chances and High-Danger Scoring Chances
As originally defined by War On Ice, 'Scoring Chances' indicate shots attempts that are taken from areas of the ice where goals are more likely to be scored. Attempts made from the attacking team's neutral or defensive zones are excluded.
Inside the zone, a shot is assigned a value of 1,2 or 3, depending on where it was from. A rebound shot (defined as any attempt made within 3 seconds of another blocked, missed or saved attempt without a stoppage in play in between) adds a point to this value. A blocked shot decreases the value by 1.
'Scoring Chances' are any shot attempts with a final value of 2 or higher. 'High-Danger Scoring Chances' are any shot attempt with a final value of 3 or higher.