Another way to look at the Penguins 2014-15 so far is to look at the shot attempts displayed on a line graph.
Here we have Corsi For and Against (shot attempts for and against) plotted out across the 41 games played so far (displayed as 10 game moving averages to smooth out the data).
The Penguins have done a pretty good job of attempting more shots than the opponent through this half of the season. You can see there are some instances where the opponent outshot the Penguins…let’s explore that more.
The picture below is the Corsi Differential (or plus/minus for you traditional statistic folks). Corsi Differential subtracts the shot attempts against from the shot attempts for (Corsi For-Corsi Against). If the differential is +3, the Penguins out-attempted the opponent by 3. If the differential is -3, the opponent out-attempted the Penguins by 3. This statistic illustrates the same data points as in the graph above, just in a different way.
As indicated by the dotted line, the Penguins out-attempted the opponent by 2 attempts, on average. However, there are two parts of the graph that dip below the zero line. These are the same points in the previous graph in which the opponent outshot the Penguins.
I also introduced another variable into this graph: PDO.
The Corsi Differential chart above shows how the Penguins did when it came to shot attempts. When we factor in PDO, which shows how the Penguins came out on the goalscoring and luck side of the picture, we get a more complete view. The line is colored red/blue to indicate PDO at that particular point in the season. Blue is lucky, red is unlucky.
PDO (the acronym doesn’t stand for anything) is the sum of Shooting % and Save %. There is lots of research that indicates that the components of PDO regresses heavily to their respective means (SV% regresses heavily to the league average, which is around 92%. SH% regresses heavily to 8%). This means that PDO also regresses to the league average of 100. PDO is commonly used as a way to measure how lucky a team is at any point in a season. Anything below 100 is bad luck, anything above 100 is good luck. Either way, you should expect it to regress back to 100.
Notice how the color shifts back and forth with no discernible pattern. The hockey gods are a finicky bunch.
We can break down how exactly PDO fluctuates by breaking it out into its component parts: Save Percentage and Shooting Percentage.
Notice how both shooting and save percentages vary wildly, with no discernible pattern. This is why the NHL is crazy and unpredictable. See also: fun and maddening.