Skip to main content

The Predictive Power of PythagenPuck

Last season I made use of the PythagenPuck formula as outlined by Alan Ryder of to make some (fortunately) successful predictions back in November that the Ottawa Senators weren't anywhere near as bad as their sub-.500 record at the time indicated, and that the Boston Bruins weren't exactly the playoff-caliber team they appeared to be according to the standings.  The basic idea was that by looking at the ratio between each team's Goals For and Goals Against totals, you get a good idea of where their actual Winning Percentage will end up.  The presumption there is that a team's overall ability to score and prevent goals is more constant than the bounces and breaks that can decide individual game results, and over the course of 82 games the "luck" will even out to a large extent.
This summer, I thought I'd revisit that analysis, to answer a few questions.
1.  Did I just get lucky, or is PythagenPuck actually a better indicator than actual Winning Percentage of where teams stand during the early part of the season?
2.  At what point does it make sense to do this kind of analysis?  After 10 games, 20, 30...?
3.  What kinds of events during the season helped make large differences in team performance and the Goals For/Against ratio?  In other words, if a GM decides that action needs to be taken, what works, and what doesn't?
First, a few ground rules to clarify my use of PythagenPuck.  Since it relates to Goals For & Against during regular action, I back out points from Shootout Wins from the Winning Percentage totals.  I then took a snapshot at each game in the regular season, and recorded each teams Actual Winning Percentage, as well as Expected Winning Percentage as given by the PythagenPuck formula based on total Goals For & Against up to that point.  For those interested in the nitty-gritty details, yes, I adjusted the exponent at each step along the way to account for the league-wide goals-per-game value as it changed during the season.
Finally, I ran correlation figures at each game along the 82-game journey between [Actual Win %(at Game X) & Final Actual Win %], and [Exp Win %(at Game X) & Final Actual Win %], and produced the following chart.
PythagenPuck correlation to actual winning percentage NHL 2006-7
What this demonstrates is that for most of the 2006-07 season, the blue line (Expected Win %) was actually more closely correlated with the final actual Winning Percentage than Actual Win % at that point in time.  Only around Game 63 do actual results take over, which makes sense because at Game 82, the values are equal to each other by definition.  So at least for last season, Question #1 would appear to be that yes indeed, PythagenPuck does indeed hold some value.  I would need to see this play out over a few more seasons before I proclaimed it to be a crystal ball, however.
As to Question #2, we have an even more interesting answer.  It looks like around the Game 15 mark, both lines reach a certain point that isn't improved upon for another 25 games or so.  In other words, absent any major disruptive issues like a key player injury or coaching change, the picture you have around the 15-20 game mark is most likely a realistic one for the course of the season.  If, as a GM, both Actual and Expected Winning Percentage aren't where you'd like them to be by mid-November, then something substantial would need to change, and the longer you wait, the less time you're left with to turn things around.  If you have a case of mixed signals, such as last November when the Senators Expected Win % was much higher than Actual results, judgment would have to come into play as to the direction of the team.
To answer Question #3, I'll follow up with a series of posts over the next week looking at some of the major moves up or down that took place through the course of the season, and see how they relate to events such as injuries, coaching changes, and trades.
There are of course, a couple refinements I'd like to make to this analysis, which I may pursue before the start of the regular season.  First, I would like to make some adjustment for the quality of opposition and it's impact on the numbers used above, and secondly, I'd like to exclude Empty Net goals from the analysis.  Empty Net goals only serve to pad the Goals For of teams that have already pretty much locked a game up, and conversely inflate the Goals Against of teams that are about to lose.  When I ran summary-level analysis and excluded Empty Netters, I did get a slightly more accurate result between Expected Win % and Actual, but I haven't had time yet to make that adjustment on my game-by-game figures that drove the analysis above.

Popular posts from this blog

How I'm Trying To Make Money Sports Blogging

To kick off this series of articles general sports-blogging articles here at OTF Classic, I think it's best to start with a comment that Brad left here last week, after I shared my goals for 2012, which include specific revenue targets:
I considered diving into the world of internet marketing myself, but I felt that my friends would hate me for bugging them about stuff. I mean, it's pretty low-risk high-reward, so it's tempting. I wouldn't mind reading about tips on how to maximize impact of blogging in general to make it a legitimate income source. Trying to make money at sports blogging can be a very touchy subject - for the vast majority of us, this is an activity we pursue to both exercise our creativity and share our love of the game, whether it's hockey, football, badminton, whatever, with fellow fans. Mixing that personal conversation with a commercial message can turn people off, especially if it becomes too intrusive for the reader.

It's not unreasonabl…

Get Your NHL Super Schedule 2008-9 Right Here!

Click here for the 2009-10 NHL Super Schedule, at my new site,!

The NHL announced the 2008-9 Regular Season schedule today, so of course, it's time right here to publish my very own NHL Super Schedule 2008-9 as well.

For those unfamiliar with what I did last year, the NHL Super Schedule is a spreadsheet that I put together and make publicly available via Google Documents*. It includes an entry for each game in each team's 82-game regular season schedule, with additional information such as how far that team has had to travel since its last game, how many days have passed since that previous game, and various statistics relative to the opponent that evening, such as 2007-8 Winning Percentage, Goals Per Game, Goals Against Per Game, etc. For example, you can total the distance that each team will travel during the upcoming season, or find who plays the most back-to-back games. Check out which team faces the toughest opposing offenses, or which power plays…

Canadian Baloney, starring James Mirtle

A tireless refrain from the Canadian media is that Nashville is an absolute failure as a hockey market, and failing to move the team north of the border is an exercise in folly by the NHL.

Our latest exhibit comes from James Mirtle, usually one of the more thoughtful hockey bloggers extant:
But Nashville, quite simply, has proven it cannot sustain an NHL hockey team. Even with the lowest ticket prices in the entire league (I know: I've looked into flying there for a game or two) and a ridiculously forgiving arena lease, the team has had attendance issues despite having one of the best records in the league.

It's not a matter of Canadians not wanting teams in the southern U.S.; I've argued time and again in favour of teams like Dallas and Tampa Bay that have supported their teams and really brought something to the table in terms of bringing news fans and new energy to the game. That's a good thing.

The Predators, however, are not that, not in the beginning and certainly no…