Saturday, February 21, 2009

Team Rankings and Playoff Probabilities


The first chart shows how each team in the league has fared thus far in terms of adjusted winning percentage. Adjusted winning percentage is essentially each team’s Pythagorean Expectation, with the exception that, instead of goals for and goals against, I use adjusted goals for and adjusted goals against. In computing each team’s adjusted GF and adjusted GA, I simply take each team’s actual GF and GA, subtract shootout goals and empty netters, and then make a second order correction for schedule difficulty. In determining schedule difficulty, oppositional strength is determined through the goal differential of the opponent, the location of the game (i.e. whether it’s a home or away game), and the circumstances of the game – namely, whether or not it’s the second half of a back-to-back for the road team.

If you compare these rankings to the actual standings, most teams are similarly positioned. There is, however, one notable outlier.

The Rangers are currently 9th in the league in points per game, yet 26th by this metric. Not surprisingly, they’ve had a ton of success in the shootout so far (record: 9-4), which is basically equivalent to sheer luck. While some may point to the Rangers shot differential, especially at EV, as evidence of them being not that bad of a team, I’m inclined to disagree. Reason being: they're in the red in terms of expected goals, which suggests that they’ve been below average in terms of shot quality for, shot quality against, or both.

Of course, there are a few teams who can be labeled as either lucky or unlucky in general – notwithstanding the fact that that these rankings aren’t too different from the standings. In other words, teams who are either better or worse than these rankings would suggest.

In terms of teams that probably aren’t as good as their adjusted winning percentage would indicate, I’m thinking of BOS, FLA, and PHI. These teams have all been greatly aided by the percentages this year. I think that the success that each of these teams has experienced thus far is unlikely to continue during the remainder of the regular season and the playoffs. Granted, the Flyers outperformed their underlying numbers last season as well. As the sample size in games played increases, it becomes increasingly difficult for one to point to randomness in an attempt to account for success with the percentages. On the other hand, I find it very difficult to look at a team that’s scored 15 shorthanded goals and conceded none and say that they haven’t been at least somewhat fortunate. I just don’t think that they're an inherently good hockey team.

And for teams in which the opposite is true, I’m thinking of OTT, LAK, COL, and TOR. These teams have all been – for lack of a better term – utterly screwed by the percentages this season, to the point where none of them have a realistic shot at making the playoffs. This is unfortunate in the sense that, if you were to compare this group of teams with the three listed above, I don’t think that there’s much to choose between them. Hell, I think that one could make a reasonable argument for the Kings being the best team of the seven – at least, looking at it in terms of which team is most likely to experience success from this point forward.

Anyway, here the playoff probabilities for all 30 teams (updated on 02/19/09). The left hand column contains seeds 1-15 in each conference, with the corresponding column for each team showing the probability of finishing the season in that position, expressed as a percentage. So, for example, the Blackhawks have an (approximately) 1% chance of finishing in 1st place in the West. The final two rows contains each team's probability of making the playoffs (in the second last row) and each team's probability of winning the division (in the last row). Future game probabilities are based on the respective adjusted winning percentages of the involved teams, game location, and whether or not the game is the second half of a back-to-back for the road team.

4 comments:

sunnymehta.com said...

BOS, WSH, and N.J haven't actually clinched a playoff spot, right? Why does it say 100 percent for them making the playoffs? Did you just round up?

And, while this won't help NYR come playoff time, I'm not totally sold that the Rangers' shootout success is pure luck. Hasn't Lundqvist always had an awesome shootout SV%?

BTW, the Flyers' ES S% is 9.3% this season but it was right at 8% last season.

JLikens said...

BOS, WSH, and N.J haven't actually clinched a playoff spot, right? Why does it say 100 percent for them making the playoffs? Did you just round up?

You're right in that those teams have not yet clinched a playoff spot.

The probabilities are based on 2000 simulations, so the 100% figure simply means that those teams made the playoffs in every single simulation. Therefore, despite the fact no team has officially clinched at this point in time, there are about 8 teams that have effectively clinched, meaning that the probability of missing the playoffs is so miniscule that it can basically be discounted.

But you're definitely correct in that this is a bit of an oversimplification. If I increased the number of simulations to sufficiently large n, then none of the above teams would make the playoffs in every simulation. For example, the probabilities at Sports Club Stats are based on 20 000 000 simulations, and while they have some teams listed at 100% , the figures are in fact rounded (Boston, for example, misses the playoffs 678 times in 20 000 000 simulations).

And, while this won't help NYR come playoff time, I'm not totally sold that the Rangers' shootout success is pure luck. Hasn't Lundqvist always had an awesome shootout SV%?

Again, a bit of an oversimplification on my part. My comment was more or less based on the fact that, at the team level, there isn't really any repeatability in shootout performance from season to season (the Rangers, for example, were 8-9 last year). Of course, the small sample size is a factor in this, in that it tends to obscure any true relationship, and teams probably do differ in their ability to win shootouts. I would agree that the Rangers most likely are a better-than-average team in the shootout , if only by virtue of having a good shootout goalie like Lundqvist. However, a good hockey team they are not.

BTW, the Flyers' ES S% is 9.3% this season but it was right at 8% last season.

True, although -- and I should have made this more clear in the original post -- my comment was more directed to the fact that the team has managed to maintain a positive goal differential over the last two seasons despite having one of the worst shot differentials in the league over that time. Their EVS% has been better than that of their opponents in both seasons.

What I find particularly interesting, though, is their PP S% -- they're first in the league in that regard this season and were tied for first last year. I'm not sure to what extent that's real and to what extent that's illusory, although the fact that they've done it two years running suggests that it's at least partly real.

Anonymous said...

Great work... Hey... how do I print these charts out, so that the entire chart is visible? I can only print out a portion of the chart.


Thanks.

Hostpph said...

most of the data they prefer to use goals because it is a good way to have a clear sight how they are doing in each game.