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08-09-2012, 02:46 PM
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Originally Posted by Czech Your Math View Post
But who relies on simple plus-minus, esp. over a full season or less, as a supreme measure of value? At most, one might use simple +/- as a supplemental stat over a full season or more. Anyone serious would use adjusted plus-minus, preferably over multiple seasons, as one of the metrics of value. On a team level, I would use GF/GA ratio or differential. One doesn't need PDO to know that a large change will usually regress towards the previous level the following year, Bill James proved that decades ago for baseball.
GF/GA is the goal in the end. You want to score more and be scored on less. But, they are a pretty small sample to draw conclusions from. Thousands of shots are better than a couple hundred goals.

I think there's too much put into stats like Corsi too. It's at least measuring something, but outshooting the opposition does not equal success. Outshoot Hasek, all you want, it might not help one bit. I think Corsi might tell you something about possession, but much less about overall effectiveness.
No, CORSI does tell you a lot about possession.

Also, I am not arguing that PDO is any kind of catch all or super stat. It is pretty much an auxiliary or supplementary tool to stats that actually mean something.

Boston was outshot two years ago, but they won the Cup. I think they'll take the goals and leave the shots for their opponents.
If that is the case, then they were “lucky” in terms of goaltending, or there was something strategic about it (i.e. take only high% shots and allow only low% shots). It doesn’t change the fact that taking even more of those high% shots is a good idea, and allowing even less of those low% shots is a good idea. In Boston’s case I would be more interested in which players were getting outshot less (i.e. relative Corsi) and who they were up against in doing so (Corsi Rel QoC)

Originally Posted by Czech Your Math View Post
I still don't see the difference. If a team is scoring 4 GPG in today's NHL, or giving up 1.5 GPG, it will also likely regress to the mean. However, if the 80s Oilers were scoring 1 GPG more than the league, I wouldn't hold your breath waiting for it to "regress to the mean." It's being proposed that PDO should be 1000 for all teams and individuals, but that's not even close to being true.

I gave examples of teams whose overall S% +SV% generally stayed above or below the mean over multiple seasons:

Islanders were 985, 986, 989, 998, and 984 the last 5 seasons.
Columbus was 990, 999, 994, 984, and 984 the last 5 seasons.
Toronto was 986, 981, 975, 997, and 998 the last 5 seasons.

These teams weren't unlucky, they were just below average. I doubt Toronto was "less unlucky", but instead was "less bad."

When Boston won the Cup two years ago, they were 1023 during the season. They improved to 1042 in the playoffs. How is that regressing to the mean? Yes, teams will regress to the mean over multiple seasons, because there's a lot of parity and teams change from year to year. They add players, they lose players, players get better, players get injured.

I gave examples of teams whose overall S% + SV% generally stayed above or below the mean over multiple seasons:

Vancouver was 1006, 1018, 1019, 1026 and 1019 the last 5 seasons.
Boston was 1004, 1036, 998, 1023 and 1019 the last 5 seasons.

Those teams weren't lucky, they were good, especially their goalies.

How is it primarily luck-driven, when the best teams tend to be higher and the bad teams tend to be lower over multiple seasons? The bad teams provide better examples in general, because it's a lot easier to be bad than good. Somehow, certain teams tend to remain lucky:

'84 1054
'85 1042
'86 1050
'87 1039
'88 1035

I know some people that will be glad to know that Gretzky was simply lucky and not great.
Teams themselves aren’t necessarily lucky. Players can be situationally lucky though. It is important to know these things when looking at a player’s GF and GA. PDO is much more useful for comparing players on the same team, IMO. I have read many good examples of this. I think it was about Koivu’s 2010 season where he was excellent but had his numbers destroyed by bad goaltending – significantly worse than what the rest of the team experienced. These kinds of things do happen within a team over the small sample size of a season. These are things PDO can catch.

Originally Posted by Czech Your Math View Post
However, if it's truly driven by randomness, wouldn't one expect the results to be unpredictable from one season to another for all teams, not just the average ones?
It is random, but not necessarily in the way you’re looking at it.

Take some player from some team. Last year he was in line with the rest of his team from a Corsi standpoint, but for whatever reason his goalie stunk at even strength when he was on the ice, posting a .882 sv% when he was otherwise .920. he was situationally unlucky, and this badly damaged his +/-. It is predictable that this will likely regress to the mean for this player. It’s not predictable that he will continue to have bad puck luck.

I see I missed an example on the linked site: 2011 Sharks. It says the Sharks were unlucky through Jan. 13 and post graphs to show how that was so. Interesting that Nittymaki (.896 overall SV%) played in 22/45 games through Jan. 13 and 2/37 after that, while Niemi (.920 overall SV%) took over in full after that. Whether Nittymaki was injured or the Sharks decided he was "unlucky", apparently this has no bearing on the matter? Good grief, if I can refute the best examples without even trying hard, how does one really take this seriously?
No, the players “doing” these events aren’t lucky or unlucky, these things are based largely on their own skill. It’s the effect on the other players on the ice that is more random and luck-based.

I think that you think this stat is trying to be something it’s not. I hate that I’m not good at explaining stuff like this.

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