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A formula for NHL team success
by Forechecker on 12/16/08 at 04:44 PM ET
Comments (6)
It’s time to get our collective geek on, and figure out which NHL teams are truly great, and which are ripe for a fall. The tool I like to use for this is called PythagenPuck, outlined in a Win Probabilities piece over at HockeyAnalytics.com (PDF). The basic idea with PythagenPuck is that a team’s Goals For and Goals Against provides a more consistent and accurate picture of their quality over the course of an 82-game season, similar to the Pythagorean Expectations invented by Bill James for baseball analysis. Early in the year, a few lucky bounces here or there can make a team look stronger or weaker in the standings than they truly are, and PythagenPuck helps identify those outliers.
I’ve provided a similar predictive look at the league in prior years, and have been pretty satisfied with the results. There are always teams which genuinely turn around their play (either for good or bad) during the course of an NHL season, but with the majority of teams, this Goals For/Goals Against analysis does a good job of identifying the high-flying frauds and the potential contenders waiting just outside the spotlight.
So here are the numbers for each team, with sage commentary included:
The Google Spreadsheet is available for public view & download.
All data through games of Sunday, December 14 2008.
In order to isolate how teams are earning Wins and Losses relative to their Goals For & Against performances, I exclude a few items from the typical NHL stats before running the numbers:
1) Points earned in Shootouts, since that action is different from regular play.
2) Points earned for Overtime Losses (OTL), so that losing 4-3 in regulation is treated the same as losing 4-3 in overtime. We’ll come back around later to point out which teams are milking the Loser Point for all its worth.
3) Empty Net goals, because they don’t so much cause wins and losses, they’re more an indicator of which teams are already going to win or lose a given game.
A consequence of items 1 and 2 above is that a game that goes to a Shootout is treated like an old-style tie (1 point for each team), which accurately reflects the result of a tied game at the end of regular action. The less-than-obvious columns in the table above are as follows:
Adj GF: Goals For, excluding empty netters.
Adj GA: Goals Against, excluding empty netters.
Adj Pts: Standings points, less the items listed above.
Adj W %: AdjPts / Games Played times 2 (Adjusted Points earned as a portion of all possible).
Exp Win %: Expected Winning Percentage, based on Adj GF & Adj GA run through the PythagenPuck formula*.
Diff: The difference between Adj W% and Exp Win%. Positive values represent teams winning more than expected (i.e. lucky). This list is sorted in declining Diff sequence, from “luckiest” to “unluckiest”.
As is my wont, the most favorable values are shaded green, the unfavorable ones pink.
In reading these results, high positive values in the “Diff” column indicate teams that have earned more Wins than their GF/GA performance would normally indicate, and thus over the long haul of the regular season, it’s likely that those Wins and Losses will pile up accordingly. Sometimes you do have a team which significantly improves or deteriorates (think Ottawa last year), but those are the exceptions, not the rule.
Besides the “Diff” column, you can also review the difference between regular Pts and AdjPts to see which teams are benefiting from the peculiarities of the NHL’s rules. The Rangers (9) and Red Wings (8), for example, have feasted on Shootout Wins and Overtime Losses to pad their place atop their respective divisions, while Phoenix and Vancouver have only snared a single point apiece through those devices.
So feel free to comb through the data here and call out your own favorite over- and underachievers in the NHL!
*The basic Pythagorean Formula runs like so: Win Pct. = GF2/[GF2 + GA2] . PythagenPuck changes the exponent from 2, to something that more accurately reflects the scoring rate in today’s NHL. The exponent used in this analysis is 2.1838. If anyone has an easy way to present the formula in HTML form, I’d be glad to hear about it, I know the formula above looks clunky.
Filed in: NHL Statistical Analysis | On the Forecheck | Permalink
Tags: pythagenpuck,
Comments
Hmm… methinks the CSS thingee doesn’t like that SUP tag. Drat!
Posted by Forechecker from Nolensville, TN on 12/16/08 at 06:06 PM ET
Then try forcing CSS…
STYLE="vertical-align: sup;”
Posted by pwnicholson from Nashville, TN on 12/16/08 at 06:12 PM ET
(I couldn’t get to the chart at work… just now getting a look at it.)
I gotta say, pet peeve again: Your chart is mislabeled- Points Percentage does not equal winning percentage.
Moving on…
Obviously your PythagenPuck has been proven to be remarkably accurate in the past, but your formula has Chicago picked as a team that is better than its record. While that may be true, their record is worse than it looks.
The high-flying Babyhawks at 15-6-7 have a strong .661 points percentage, but in reality they are a .535 team (15 wins, 14 losses). Take away 3 skills competition ...er… shootout wins for the ‘Hawks and the numbers look even worse, with Chicago winning only 12 games out of 28 in actual hockey play (win or OT win). How then do you figure in the above chart that they are .589 when taking out shootout and OTL points (i assume by this you mean that a shootout win counts as 1 point and OTL counts as a real loss for 0 points)? Shouldn’t they be a .428 team in “real” record?
Posted by pwnicholson from Nashville, TN on 12/16/08 at 10:15 PM ET
If you look at the “HardCore” tab on the Google Spreadsheet, it has a little more detail. I show Chicago with 2 Shootout Wins and 2 Overtime Losses, which would turn their 15-6-7 record into 13-8-7 under the old W-L-T methodology, which yields the .589 “points percentage” (your terminology is undoubtedly more correct).
What this translation does is turn any game that goes to a shootout, win or lose, as the equivalent of a Tie (1 point) earned in regular play, because after 65 minutes of team hockey, the teams remain even. The shootout is basically a crowd-pleasing bonus point. Chicago, in this case, is 2-5 in the shootout, which turns into 7 ties.
That’s one nice aspect of PythagenPuck, is that it handles the single point for ties rather elegantly. Going back to the old format would make for easier analysis on my part, but I understand that fans dig the shootout, so it’s here to stay.
Posted by Forechecker from Nolensville, TN on 12/16/08 at 11:32 PM ET
Thanks for putting it together putting it all together. Pulling out the OTL, SOL and ENGA is a bit tedious.
I had not looked at the Pythagorean Standing in a while. While ATL has been a bit unlucky of their GF/GA they also have a “lucky” Even Strength Save Percentage so far this year. If you take the “luck” out of GF/GA and give some weight to SF/SA I suspect ATL probably would not rank at the bottom anymore.
The Rangers fans are complaining but it is more bad luck than anything. Some of the Rangers are just getting stoned so far at E.S. That should regress to the mean.
Posted by The Falconer from Atlanta on 12/20/08 at 05:38 PM ET
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About On the Forecheck
Dirk Hoag is the Forechecker, churner of NHL stats and analysis. Having started over 10 years ago writing for websites like In the Crease and e-Sports, Dirk launched On The Forecheck in 2005 to cover the Nashville Predators as well as apply statistical analysis to NHL hockey.
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Just use the tag <sup> for making something superscript.
I would show you, but KK’s engine doesn’t support it in comments, at least.
Posted by pwnicholson from Nashville, TN on 12/16/08 at 05:29 PM ET