STATISTICAL ANALYSIS | When judging the performance of a player, most of us rely primarily on what we see on the ice. We observe John Carlson struggling, we notice Alexander Semin's level of caring and Tomas Vokoun's focus (or lack thereof) in net. But as we’ve discussed before, your eyes can deceive you, especially when it comes to the percentages at play over the course of a hockey season. This is especially true when dealing with the impact of “puck luck” and its effects on the game.
Luckily there is PDO, a metric named after the screen name of its inventor, Brian King, that helps us sort this out.
PDO is a simple statistic. For an individual, it is the summation of a team's shooting and save percentage when the player is on the ice during even strength.
For example, when Alex Ovechkin has been on the ice during even strength this season, the team has a shooting percentage of 8.2 percent and has saved shots at a rate of .917. So that makes his PDO value 999 (.082+.917=.999), which is almost exactly the league average. In other words, Ovechkin has seen neither very good nor very bad “puck luck” this season.
What’s useful about this metric is that it’s “unstable,” and over a large-enough sample will regress to 1000. Why 1000? Because every shot that is a goal is a shot not saved, and vice versa.
Because of this, we can use PDO to determine whether a skater's performance over the course of a small sample (say, 48 games prior to the All-Star break) is likely to continue or not.
In Washington's case, there is a mixture of optimism and caution.
There are three offensive players who should see their production slow down over the rest of the season: Mathieu Perreault, Marcus Johansson and Troy Brouwer. All three have a PDO value of more than 1010, mostly fueled by abnormally-high shooting percentages. Perreault is the most extreme example, on ice for a 13.2 percent shooting percentage when the league average is closer to eight percent. In other words, these players have had some unusually good fortune when it comes to being on the ice when pucks are going in net.
Mike Knuble and Matt Hendricks, on the other hand, have very low PDO values, and should start to see their fortunes change. No goat sacrificing required.
On the defensive side of the puck, is there a player more snake bit lately than Carlson? The netminders are saving just .903 of the even-strength shots when he is on the ice but .925 when his frequent partner Karl Alzner is on for a shift. We saw this before with Roman Hamrlik, and then things started to go Hamr’s way and he didn't look as bad. I expect to see the same in Carlson’s numbers over the next few games.
And finally, the one player I think fans will say, “Man, did he really pick up his game after the All-Star break” is Brooks Laich. He is not getting a ton of “puck luck,” having converted just eight percent of his scoring chances (NHL average is 14 percent) despite generating them against tough competition. If you are in a fantasy pool or just want to look cool to your friends, start letting them know he is your pick for a fantastic rest of the season.
Follow Neil on Twitter: @ngreenberg