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08-15-2012, 09:19 AM
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Originally Posted by Czech Your Math View Post
I found the data relating to PDO, although I have concerns about its reliability. When I calculate the Shooting%s using their GF/60 and SF/60 data (and GA & SA), the results do not generally match the numbers provided.

However, assuming their data is correct, I see the following:

1) There is a fairly strong correlation (over 60%) for opponents' shooting% (S%A) from one season to the next. Since SV% = 1 - S%A, this component of PDO does not seem close to being "almost entirely driven by luck."

2) S%A is much less and negatively correlated to the current season's SA/60. So as the opponents' shots rise, the team's S%A falls, which increases SV%, which increases PDO. Since a team which is giving up a lot of shots is considered my many to be "outplayed" (outshot), and their SV% will be higher on average (due to the correlation described), and they will be considered a bit "luckier" due to a generally higher PDO.

3) As others have said, and I may have been incorrect about, a team's shooting% 5v5 appears to be rather unpredictable. I would like to verify the data before concluding this, however. There is a small negative correlation between SF and S%F, so again a team be considered by some to be "outplaying" their opponent, while being a bit "unlucky", but this is not too significant. There is a much stronger correlation between overall S%F from season to season. I would guess the reason for this, is that the players on the PP are of much higher skill, so that their shooting%s are much more predictable from one year to the next.

4) PDO itself is somewhat correlated to the PDO from the previous season (as measured by the difference between 1000). The correlation is much stronger (over 50%) for overall PDO.

Conclusions- As I already said, I hesitate to conclude much more without the BTI's data being verified as correct. However, it seems to me that:

A) On a team level 5v5 PDO may be a product of mostly random factors and therefore could be of some use in determining the sustainability of team ES goal differential.

B) On an individual level, 5v5 PDO may also be a product of mostly random factors, but this may vary significantly by individual. It's probably especially useful for 3rd/4th line grinders, who have limited skill, as compared to top liner players whose S%F is going to be much more influenced by that line's superior skills.

C) Overall team PDO seems to be much more predictable and may be at least as much due to skill as luck. When teams have their best players on the PP & PK, the cream rises to the top much more.

D) Since the metric is used to determine the sustainability of an individual player's plus-minus, the top line players' roles on the PP & PK must also be considered, as these roles may significantly influence their plus-minus numbers (through SHG F & A).

I would like to look further at PDO, but am waiting for confirmation that the data is reliable in order to do any further study on this.
Thanks for taking the time to do this.

With respect to point B) I have always felt that the leagues elite players tend to be almost de facto outliers with respect to many of the more popular statistical manipulations.

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