Hello everyone and welcome to Arctic Ice Hockey's very own Friday #FancyStats Mailbag! Once a week I'll be answering a few of your questions on underlying metrics. Also, I will try to explore any concerns about the Jets that can be investigated through data.
Jeff writes:
I was wondering if you'd seen anyone look at goalie strength of opposition. I wanted to find a statistical answer to the question "do back up goalies get easier starts?" The anecdotal evidence says yes, but I wanted something more concrete. I couldn't find it as a stat on any of the analytics sites I frequent. I asked around on twitter too but haven't found anything.
There have been a few times this has been looked at.
Jonathan writes:
Does anyone track shooting percentage for shot attempts not solely shots on goal? Does this prove to be more stable year to year than typical shot percentage?
Shooting percentage for shot attempts (or Corsi) and non-blocked shot attempts (or Fenwick) are available. This is also true for save percentage as well. You can find this type of information for players and teams on most underlying metrics websites like War on Ice or Puckalytics.
When conducting analytical research, percentages from non-blocked shot attempts are actually superior tools, but normally we talk about shooting percentage and save percentage in terms of shot on goals due to traditions. One of the primary reasons why it works out better is the larger sample size of data, leading to less variance from sampling error.
Because of this decrease in variance, it would be more stable from year to year. The rarity of goals and the natural variance of goaltending though still makes any percentage extremely unstable.
Cara writes:
I’m concerned about Jacob Trouba. He has had a slow start to the season and although this must be partially due to his partnership with Mark Stuart, he doesn’t look as with it as last year. I know it’s early in the season, but the Jets defence is paper thin and this seems like a major problem. How concerned should I be?
There has been a lot of talk about the "sophomore slump" for Jacob Trouba, but I'm still not sure how much is valid and how much may just be bad bounces. From the eye-test he seems to have struggled a bit and even picked up a few of Mark Stuart's bad habits, but let's take a look at the numbers.
There is some legitimacy to the concerns. Last season Trouba had a 49.4% open-play Corsi% and 48.4% when exclusively paired with Stuart. This season This season Trouba has posted a 45.8% open-play Corsi% with and without his partner Stuart (although his without sample is just under 35 minutes).
Part of this may be from added responsibility. Last year the Stuart-Trouba pair started the season as the Jets sheltered minutes pair, with Enstrom-Bogosian and Clitsome-Byfuglien taking the tough minutes. It wasn't until nearly two-thirds through the season that Stuart-Trouba started picking up more top six match ups and more defensive zone starts.
As long as Trouba is beside Stuart there will be some anchoring effect needed to be taken into account. In nearly the same number of minutes, Zdeno Chara -in his prime where he was arguably the best shot metrics defenseman in the league- posted a 47.3% open-play Corsi% with Mark Stuart.
However, we should see some opinions return to normal on the young defenseman in time. Currently the Jets have a 95.6 PDO with Trouba on the ice. In other words, Trouba's goal differential output of 27.3% under values his true input. If he continues performing at the same level, we will most likely see that output improve and move towards his open-play Corsi% as the sample increases.
Thank you everyone who wrote!
That is all for this week. If I didn't get to your question this week, I promise I will eventually reply. The plan is to answer every single question given to me, although sometimes they may slide a week or two depending on the load of questions I receive.
If you have any questions you want looked at, email me at garrethohlaih (at) gmail (dot) com.
