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01-03-2013, 09:47 AM
Czech Your Math
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The variations are relatively small, but what likely caused the larger variations between the model and actual measurements? Sometimes extreme values for one or more of the variables aren't fully captured by the model, or it could be another factor that is difficult to quantify at all. Let's briefly examine the largest differences:

1972 (+3.5%): The GAG line of Ratelle-Hadfield-Gilbert finished 3-4-5 behind Espo & Orr. Xt (which captures offensive powerhouse teams) has its second highest value during the 44 seasons since O6 expansion, despite Xf (stdev of team GF, which is the denominator for Xt) being at its third highest level in the study. Basically, it's difficult to fully capture just how top-heavy the league was that year.

1977 (-4.2%): It appears there was a real lack of depth in the top 1N. There's Lafleur and Dionne at the top, but no longer Espo & Orr & Co. and not yet Trottier & Bossy. Some indications of the weak depth are Shutt, MacLeish and Tim Young 3-4-5, and the top 1N containing Ratelle & Espo in their mid-30s and d-men Robinson & Potvin.

1980 (+4.0%): While the WHA teams were only 4/21 of the new NHL, 4 of the top 11 point producers were from the former WHA (including of course Gretzky who tied for the lead.

1983 (-3.1%): Tough one to explain. PPO/game were at the lowest level for the period '81-'09, so that may not have been fully captured in the variable.

1987 (-3.2%): Previously elite players like Dionne, Trottier, Bossy and Stastny were no longer near the top, while Lemieux and Yzerman were yet to hit their peaks. It was also a time when parity hit its heights, as Xf (stdev of team GF) was the lowest and Xa (stdev of team GA) was the second lowest value in the 44 seasons since O6 expansion.

1990 (+3.2%): The only thing that strikes me is that the old guard (Gretzky, Lemieux, Yzerman, Messier) were still strong, while the new guard (Hull & Oates, Turgeon, Lafontaine, Sakic) emerged.

1992 (-3.6%): This is one of toughest variations to explain. Basically, Gretzky finally passes his peak, Lemieux misses 20% of the season (but that's typical) and the other stars didn't really step up and have career years (as they would in '93). While the American players had really become a force, the non-N.A. players were not really a factor in the top 1N (Fedorov snuck in at #22 and Mogilny just outside at #24), they and the American players (as well as only one added team since WHA merger) were providing more depth outside the top 1N, which probably caused league GPG to be higher than it otherwise would have been (which lowers the adjusted numbers for the top players).

1996 (+5.7%) and 1997 (+3.7%): None of the values of the variables stands out, but what does is the number of superstars who were entering or still in their prime during these years. Just look at the top 10 in total points in '96+'97: Lemieux, Jagr, Selanne, Francis, Kariya, Forsberg, Gretzky, LeClair, Lindros and Sakic. Francis was playing with Jagr at ES (and with Lemieux at ES in '97 and on the PP both years) and LeClair was playing with Lindros. Rounding out the top 1N was a mix of players from the US (Weight, Tkachuk, Hull? and Modano), overseas (Mogilny, Palffy, Sundin, Fedorov, Nedved) and the usual Canadians (Messier, Turgeon, Yzerman, Damphousse, Oates, Shanahan and Fleury). Just missing the cut were players such as Recchi, Bondra, Gilmour, Kamensky, Brind'Amour, Amonte and Roenick. So it's no surprise that the top 1N outperformed expectations in these years.

2000 (-4.1%) & 2002 (-3.4%): Power plays were the lowest and third lowest, respectively, for the period '86-'09. Lemieux and Gretzky were gone, Messier and Hull were no longer factors. Injuries started to take their toll on Lindros, Forsberg, Mogilny, Palffy, etc. There wasn't yet a strong crop of younger players to take the places of all these retired, aging and injured stars.

2006 (-3.3%): The only extreme value among our variables is the historically high level of power plays. This may have exaggerated expectations, at least in part for the following reasons (which had various effects on their own as well): This was a very dynamic season, as it followed a lockout season and there was a dramatic change in rules enforcement. Many players either retired during the lockout, did so during the season, were with new teams, or were rusty from playing little or no hockey during the lost season (and what hockey they did play was with different players in a different environment). When conditions change so drastically overnight, it's neither surprising nor concerning that there would be a variation between predicted and actual performances.

2007 (+4.6%) & 2008 (+4.1%): Power plays were at a more moderate level, especially by '08, yet play may was probably still more open due to the crackdown in '06. While there were new stars (Ovechkin & Malkin) at the top, there were also many players in their prime (Dastyuk, Thornton, Lecavalier, Spezza, Zetterberg, Kovalcuk, Gaborik) and some older 30+ players having very good seasons (Iginla, Alfredsson, Kovalev, St. Louis).

I believe the variations are generally surprisingly small, given the randomness inherent in such data and the many effects that are very difficult or impossible to properly quantify. It seems that most of the relatively larger variations between predicted and actual have reasonable, logical explanations. I'm satisified with the results of this study at this point and believe it provides solid support that adjusted points are very practical for comparing offense across seasons in the post-expansion era.

Last edited by Czech Your Math: 02-23-2013 at 11:36 AM.
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