Sunday, August 27, 2006

Adjusted Assist Scoring: Single Season

In sabermetrics and hockey one problem is to adjust scoring between different eras. The hockey outsider has a method to do this that I have already used to look at single season adjusted goals and am mostly satisfied with the results.

Adjusting assists is slightly different than adjusting goals because the frequency of asists being given out by scorers has changed significantly over time. In the earoy days of hockey, there were more goals than assists. Most goals were unassisted. Today, most goals have two assists. This gives one more factor that needs adjustment.

Here are the top 10 adjusted assist seasons according to the hockey outsider (Peter Albert):

Top 10 Adjusted Assist Scoring Seasons of All Time
Name Team Year Games Played Adjusted Assists Actual Assists
Wayne GretzkyEdm1985/8680129163
Cy DennenyOtt1924/252812815
Duke KeatsEdm- WCHL1921/222511925
Bill BoucherMon1924/253011013
Wayne GretzkyLA1990/9178109122
Wayne GretzkyEdm1984/8580107135
Dick IrvinChi1926/274410618
Wayne GretzkyEdm1986/8779103121
Howie MorenzMon1927/284310318
Frank BoucherNYR1928/294410316

This list is not nearly as satisfactory as the adjusted goals list. It contains Wayne Gretzky four times. Since he has far more assists than anyone else in history this is not suprising. The problem is the other six guys on the list are all from the 1920's. Until the 1929/30 season, there was a maximum of one assist per goal and the scorer would only give out an asists if he though it clearly led to the goal. This can clearly be seen looking at the all time assist leaders by season. Frank Boucher lead the NHL in assists in both 1929 and in 1930 (after the change was made to today's system). In 1929 he has 16 assists (good enough for 10th all time on the hockey outsider list). In 1930 he had 36 assists but now placed 23rd on the hockey outsider list. That is an amazing piece of normalization. In back to back years a player gets 20 MORE assists but is normalized to have more normalized assists in the year when he had 20 LESS assists.

These 1920's players at the top of the list are due to normalization effects. They benefit because their games played was low and they benefit because there were few assists. Each real assist Cy Denneny got in 1925 was worth more than 8.5 normalized assists. Each real assist that Wayne Gretzky got in 1986 was worth less that 0.8 of a normalized assist. Was a Cy Denneny assist really worth about ten Wayne Gretzky assists to his team? Obviously it wasn't. This is a false normalization problem. I will write in the future about this and why it dominates this normalized assist list.

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