ABOUT POINT SHARES
The Point Shares system is based on the fact that marginal goals for and marginal goals against are linked to team points.
At the team level, marginal goals for and marginal goals against are equal to:
MGF = (team goals) – (7 / 12) × (team games) × (league goals per game)
MGA = (1 + (7 / 12)) × (team games) × (league goals per game) – (team goals against)
Marginal goals for and marginal goals against can be converted into expected points using the following formula:
Expected Points = (league points per goal) × (MGF + MGA)
A player can have negative Point Shares. I justify this by thinking about it in the following way: a player with negative Point Shares was so poor that he essentially took away points that his teammates had generated.
Offensive Point Shares are credited to skaters based on goals created and time on ice.
Goalies will receive 2/7 of the team's defensive point shares, on average, although that fraction is adjusted upward or downward in seasons where shots against are available.
The final step of the process is to find the sum of Offensive Point Shares (OPS), Defensive Point Shares (DPS), and Goalie Point Shares (GPS) for each player.
Because this metric is designed to estimate a player’s contribution in terms of points, it makes sense to see if the sum of player Point Shares for a particular team closely matches the team’s point total. Looking at all NHL teams from 1917-18 to 2009-10, the average absolute error is 5.05 points per 82 games and the root mean squared error is 6.64 points per 82 games.
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