Monday, 22 September 2014

Year to Year Repeatability of New Goalie Stats

For as long as people have been analyzing hockey, goalies in particular have been difficult to analyze. Based on what information has been available to the masses up until now, it has been extremely difficult to get an accurate read on a goalie's abilities until they see a large amount of action. Metrics in evaluating goalie performance to date have ranged from awful (wins and GAA) to informative but unpredictable (SV%). However, a new hockey statistics site called War-On-Ice has released data that has been able to further break down a goalies SV% into more detailed categories depending on the shot location data provided by the NHL. Their four new stats (and one more classic stat) are as follows:
  • Low Save Percentage
  • Medium Save Percentage
  • High Save Percentage 
  • Adjusted Save Percentage
  • UnAdjusted Save Percentage (technically not new since it's just basic SV%)
While these new metrics are definitely very descriptive and informative I really wanted to test the predictive value in goalie projections. That is, if a goalie posted a .900 SV% in a certain category last year, what should we expect them to get next year?
Save Percentage Zones via war-on-ice.com
The picturing above shows the zone breakdown for each of these stats:
  • Blue = high percentage shots (SvPctHigh)
  • Red = medium percentage shots (SvPctMedium)
  • Yellow = low-percentage shots (SvPctLow)
Here is the breakdown of how these stats matched up versus one another from one season to the next. (Regression line in red)


Well, that wasn't very informative. We see very little correlation from one season to next regardless if you're treating every shot as equal (Unadjusted SV%) or break each shot down by it's general degree of difficulty (Low, Med, High SV%). I had high hopes for Adjusted Save% too (especially after I first ran these numbers and found some interesting results before realizing I had completely screwed up my data, idiot).

Adjusted Save% is still quite interesting in my eyes as explained in the War-On-Ice Glossary:
AdjustedSvPct: The weighted average of Low, Medium and High Save Percentages, as weighted by the league average frequency of each shot type. Compare to statistical benchmarking -- correcting a simple random sample for known stratification issues.
And from one of the creators, A.C. Thomas:
Here's a table with the results (we want RSQ to be close to 100% and p-value to be less than 0.05):


Type Count Shots Faced AdjustedRSQ RSQ p-value
UnAdjusted 99 >1500 1.72% 0.70% 0.196
Adjusted 99 >750 0.11% 1.14% 0.294
Low 77 >500 2.02% 3.31% 0.1134
Med 80 >300 -0.14% 1.13% 0.3482
High 103 >200 7.81% 8.71% 0.00247

**The Count column is simply the number of observances for each type of Save%. Shots faced is the arbitrary number of shots I made as a cut off point. Ex. For a goalie's LowSvPct to be counted, they would have to have faced more than 200 shots from the designated Low area of the ice in back-to-back years. This happened 77 times between 2008 and 2014 or an average of ~15 goalies per pair of years. Also, these stats are just even-strength (5v5).

The best results here were clearly for SvPctHigh, which is for shots directly in front of the next (in the slot). While the correlation is still small, it seems better than most results we see when it comes to goalie metrics. So maybe there is a little something to a goalies ability to defend a likely scoring chance.

Obviously, when using this method you observe some survivor bias as goalies who see lots of action in back-to-back years will tend to be of the higher caliber to begin which can result in some bias. Maybe I will revisit this later and try to simply weight goalies based on their shots faced instead of simply ignoring those below an arbitrary threshold. Until then, it seems like goalies will remain one of hockey's greatest enigmas. 

33 comments:

  1. Thank you very Steady info ... hopefully more successful.
    Pengobatan Herbal Jantung

    ReplyDelete
  2. This is quite easy to write cover letter for civil engineer job application only if you are est writer. This is very important thing that you do before getting the job.

    ReplyDelete
  3. Thanks for the information. Once very beneficial to us all. Awaited further information.
    Efek Samping Brain Care Capsule

    ReplyDelete
  4. Thanks for the information. Once very beneficial to us all. Awaited further information.

    Obat Tradisional Batu Empedu
    Cara Mengobati Sperma Kosong

    ReplyDelete
  5. Thanks for the information. Once very beneficial to us all. Awaited further information.

    Cara Menurunkan Berat Badan Tanpa Olahraga

    ReplyDelete
  6. Thanks for the information. Once very beneficial to us all. Awaited further information.
    Obat Tradisional Keputihan Gatal dan Perih
    Agen Qnc Jelly Gamat Kota Semarang

    ReplyDelete
  7. Thanks for the information. Once very beneficial to us all. Awaited further information.
    Gejala Penyebab Btu Ginjal dan Cara Pengobatannya

    ReplyDelete
  8. Thanks for the information. Once very beneficial to us all. Awaited further information.
    Obat Tradisional Keputihan Gatal dan Perih
    Harga Super Nutrition Green World

    ReplyDelete
  9. thnks for your information. thats so good
    please visit me in here Harga Ganoderma Plus Capsule

    ReplyDelete
  10. I think this is an informative post and it is very useful and knowledgeable. therefore, I would like to thank you for the efforts you have made in writing this article

    penyebab haid tidak lancar
    cara mengobati diare
    cara mengobati mata bengkak
    cara menurunkan darah tinggi
    cara menyembuhkan cacar air

    ReplyDelete
  11. Sharing valuable content, this is what I need to know. Thank you once again, i thanks for sharing this good content here.

    penyebab kaki bengkak pada ibu hamil

    ReplyDelete
  12. My ex-husband and I had always managed to stay friendly after our divorce in February 2017. But I always wanted to get back together with him, All it took was a visit to this spell casters website last December, because my dream was to start a new year with my husband, and live happily with him.. This spell caster requested a specific love spell for me and my husband, and I accepted it. And this powerful spell caster began to work his magic. And 48 hours after this spell caster worked for me, my husband called me back for us to be together again, and he was remorseful for all his wrong deeds. My spell is working because guess what: My “husband” is back and we are making preparations on how to go to court and withdraw our divorce papers ASAP. This is nothing short of a miracle. Thank you Dr Emu for your powerful spells. Words are not enough. here is his Email: emutemple@gmail.com or call/text him on his WhatsApp +2347012841542    

    ReplyDelete
  13. I think this is one of the most significant information for me.
    And i’m glad reading your article.
    wordpress
    blogspot
    youtube
    មាន់ជល់

    ReplyDelete