For goaltenders, GGVT is the same as GVA.
I've been looking at simulating goaltender performance and calculating GVA and GVT. Here, I look at actual GGVT compared to actual GVA and the simulation data for GVA. For example, in 2009 Roberto Luongo had a observed GGVT of 11.1 and an observed GVA of 9.03. Simulating his workload, I found that GVA had standard deviation of 12.58 at that workload. Thus a 95% confidence interval for his GVA is [33.68, -15.62]. Since Luongo's GGVT falls in this interval, it is statistically the same as his GVA.
I compared actual GGVT to the calculated confidence intervals for GVA for all 434 goaltenders who played at least 1 game from 2005 to present. The 2009-2010 data is presented in full in Appendix A below. The data for all seasons is here http://spreadsheets.google.com/ccc?key=0An-GS2MUpN1mdFJsZE1veTU4a1o3cjRwTlEtMW43a3c&hl=en&authkey=CP7-uq8F Every single one of the 434 actual GGVT values observed fell within the corresponding 95% confidence interval for GVA.
In most cases, the differences between actual GGVT and GVA are small. There are 30 goalies for whom the difference is greater than 10. 28 of them are from 2005 and 2006. The other 2 are from 2008. For example, Martin Gerber in 2005 has the greatest difference. His actual GGVT was 11.8 but his GVA was -10.4 for a difference of 22.2. I calculate a GGVT* of -3.64, which is a lot closer to his GVA. I have listed the 30 goaltenders, their actual GGVT, GVA, and calculated GGVT* in Appendix B. I am unable to explain why 28 of the 30 most extreme discrepancies occur in those 2 years.
If you compare observed GGVT to the distribution of GVA generated by average goalies, observed GGVT looks more like GVA than GVA itself. Of the 434 observed GGVT values, 31 fell above the average goalie 95% CI, 8 fell below the average goalie 95% CI, and 405 fell within the average goalie 95% CI. For GVA, the numbers were 24 above, 41 below, and 369 within. Thus more of the actual GGVT values fell into the average goalie GVA confidence interval than did actual GVA values.
55 goaltenders have a GVA > actual GGVT. 2 goaltenders, Bryzgalov in 2009 and Halak in 2009 had a GVA that was above the average goalie CI while their actual GGVT was within the average goalie CI.
Why is GGVT the same as GVA? GGVT is defined relative to threshold save percentages while GVA is defined relative to average save percentages. Comparing the values:
|
Even Strength |
Penalty Kill |
Power Play |
Overall |
|
|
NHL Average |
0.917 |
0.868 |
0.914 |
0.909 |
|
Calculated Threshold |
0.914 |
0.863 |
0.911 |
0.905 |
|
Required Shots 80% Power |
134930 |
73094 |
139262 |
82757 |
Sample sizes for binomial distribution testing are reasonably easy to calculate. For a given pair of probabilities we can calculate the number of trials needed to see a difference in the two probabilities. Imagine we had a group of “average” goalies and a group of “threshold” goalies. For p1=0.917 and p2=0.914, to have an 80% probability of seeing a difference, the required number of shots each group would need to face calculates as 134930. The table above shows the results for the other pairs of probabilities.
Conclusion
GGVT is statistically indistinguishable from GVA. The threshold save percentages used to calculate GVT are statistically indistinguishable from the average save percentages used to calculate GVA.
Acknowledgments
Again, I want to thank Sunny Mehta for his very helpful correspondence. I also want to thank Tom Awad again for his patient and thoughtful discussions of GVT.
Appendix A
GGVT: GGVT from Tom’s tables
GVA: GVA calculated as before
StdDev: standard deviation of GVA derived from the simulations
Upper CI: Upper limit of the 95% CI for GVA
Lower CI: Lower limit of the 95% CI for GVA
|
Year |
Name |
GGVT |
GVA |
StdDev |
Upper CI |
Lower CI |
|
2009 |
AndersonCraig |
18.50 |
19.36 |
13.73 |
46.27 |
-7.55 |
|
2009 |
AuldAlex |
-5.60 |
-8.99 |
7.11 |
4.94 |
-22.92 |
|
2009 |
BacklundJohan |
0.20 |
0.14 |
1.39 |
2.87 |
-2.59 |
|
2009 |
BackstromNiklas |
-3.50 |
-9.75 |
11.65 |
13.09 |
-32.59 |
|
2009 |
BernierJonathan |
3.90 |
4.55 |
2.77 |
9.98 |
-0.88 |
|
2009 |
BironMartin |
-7.20 |
-8.81 |
8.41 |
7.68 |
-25.30 |
|
2009 |
BoucherBrian |
-3.40 |
-7.57 |
8.09 |
8.29 |
-23.43 |
|
2009 |
BrodeurMartin |
13.70 |
11.51 |
12.92 |
36.84 |
-13.82 |
|
2009 |
BrodeurMike |
4.20 |
5.20 |
2.70 |
10.48 |
-0.08 |
|
2009 |
BryzgalovIlya |
23.60 |
25.44 |
12.81 |
50.55 |
0.33 |
|
2009 |
BudajPeter |
3.30 |
2.76 |
5.63 |
13.80 |
-8.28 |
|
2009 |
ClemmensenScott |
2.40 |
1.43 |
7.41 |
15.96 |
-13.10 |
|
2009 |
ClimieMatt |
-1.20 |
-1.74 |
1.71 |
1.62 |
-5.10 |
|
2009 |
ConklinTy |
10.00 |
11.26 |
8.03 |
27.01 |
-4.49 |
|
2009 |
CrawfordCorey |
0.20 |
0.15 |
1.69 |
3.47 |
-3.17 |
|
2009 |
CurryJohn |
-3.00 |
-2.92 |
0.99 |
-0.97 |
-4.87 |
|
2009 |
DanisYann |
2.50 |
2.58 |
4.12 |
10.65 |
-5.49 |
|
2009 |
DeslauriersJeff |
-7.50 |
-12.20 |
11.21 |
9.77 |
-34.17 |
|
2009 |
DipietroRick |
-0.80 |
-2.37 |
4.01 |
5.48 |
-10.22 |
|
2009 |
DubielewiczWade |
-1.40 |
-1.73 |
1.72 |
1.64 |
-5.10 |
|
2009 |
DubnykDevan |
-8.10 |
-10.38 |
6.87 |
3.09 |
-23.85 |
|
2009 |
DuchesneJeremy |
-0.50 |
-0.62 |
0.59 |
0.53 |
-1.77 |
|
2009 |
ElliottBrian |
3.70 |
2.12 |
10.86 |
23.41 |
-19.17 |
|
2009 |
EllisDan |
1.10 |
0.00 |
8.35 |
16.36 |
-16.36 |
|
2009 |
EmeryRay |
0.40 |
-1.83 |
8.10 |
14.05 |
-17.71 |
|
2009 |
EnrothJhonas |
-0.50 |
-0.67 |
1.77 |
2.80 |
-4.14 |
|
2009 |
ErsbergErik |
0.10 |
-0.01 |
4.48 |
8.77 |
-8.79 |
|
2009 |
FleuryMarc-Andre |
0.00 |
-4.12 |
12.22 |
19.83 |
-28.07 |
|
2009 |
GaronMathieu |
-1.40 |
-3.62 |
8.45 |
12.94 |
-20.18 |
|
2009 |
GiguereJean-Sebastien |
0.50 |
-0.36 |
9.24 |
17.75 |
-18.47 |
|
2009 |
GreissThomas |
2.10 |
1.33 |
5.74 |
12.59 |
-9.93 |
|
2009 |
GustavssonJonas |
-4.10 |
-7.24 |
9.81 |
11.99 |
-26.47 |
|
2009 |
HalakJaroslav |
20.20 |
21.08 |
10.70 |
42.06 |
0.10 |
|
2009 |
HardingJosh |
-1.10 |
-3.05 |
7.56 |
11.76 |
-17.86 |
|
2009 |
HedbergJohan |
10.10 |
10.36 |
10.53 |
31.00 |
-10.28 |
|
2009 |
HillerJonas |
18.30 |
18.48 |
12.33 |
42.64 |
-5.68 |
|
2009 |
HowardJimmy |
24.70 |
27.12 |
12.27 |
51.17 |
3.07 |
|
2009 |
HuetCristobal |
-10.20 |
-14.60 |
9.40 |
3.82 |
-33.02 |
|
2009 |
JohnsonBrent |
0.10 |
-1.49 |
6.63 |
11.51 |
-14.49 |
|
2009 |
JohnsonChad |
1.40 |
1.20 |
3.32 |
7.71 |
-5.31 |
|
2009 |
KhabibulinNikolai |
1.00 |
0.10 |
7.09 |
14.00 |
-13.80 |
|
2009 |
KhudobinAnton |
2.80 |
3.58 |
2.02 |
7.54 |
-0.38 |
|
2009 |
KiprusoffMiikka |
23.00 |
25.08 |
12.97 |
50.50 |
-0.34 |
|
2009 |
LaBarberaJason |
8.30 |
9.65 |
6.30 |
22.00 |
-2.70 |
|
2009 |
LalimePatrick |
0.20 |
0.13 |
5.98 |
11.85 |
-11.59 |
|
2009 |
LeclairePascal |
-12.50 |
-15.85 |
8.37 |
0.55 |
-32.25 |
|
2009 |
LegaceManny |
0.90 |
-1.35 |
7.83 |
14.00 |
-16.70 |
|
2009 |
LehtonenKari |
1.30 |
1.26 |
5.38 |
11.81 |
-9.29 |
|
2009 |
LeightonMichael |
0.10 |
-2.48 |
8.67 |
14.51 |
-19.47 |
|
2009 |
LundqvistHenrik |
25.70 |
24.55 |
13.05 |
50.13 |
-1.03 |
|
2009 |
LuongoRoberto |
11.10 |
9.03 |
12.58 |
33.68 |
-15.62 |
|
2009 |
MacDonaldJoey |
-1.90 |
-2.43 |
3.64 |
4.71 |
-9.57 |
|
2009 |
MasonChris |
11.00 |
9.60 |
11.92 |
32.97 |
-13.77 |
|
2009 |
MasonSteve |
-5.60 |
-10.88 |
11.91 |
12.46 |
-34.22 |
|
2009 |
McElhinneyCurtis |
-1.50 |
-1.98 |
6.61 |
10.99 |
-14.95 |
|
2009 |
MillerRyan |
36.70 |
40.12 |
13.10 |
65.80 |
14.44 |
|
2009 |
NabokovEvgeni |
27.90 |
30.38 |
13.64 |
57.11 |
3.65 |
|
2009 |
NeuvirthMichal |
2.90 |
2.10 |
6.11 |
14.08 |
-9.88 |
|
2009 |
NiemiAntti |
4.30 |
4.03 |
8.88 |
21.44 |
-13.38 |
|
2009 |
NiittymakiAntero |
3.30 |
3.34 |
10.80 |
24.51 |
-17.83 |
|
2009 |
OsgoodChris |
-8.70 |
-12.33 |
6.83 |
1.06 |
-25.72 |
|
2009 |
PavelecOndrej |
-0.50 |
-2.10 |
10.65 |
18.77 |
-22.97 |
|
2009 |
PechurskiAlexander |
0.20 |
0.23 |
1.05 |
2.29 |
-1.83 |
|
2009 |
PetersJustin |
-0.20 |
-1.21 |
4.41 |
7.42 |
-9.84 |
|
2009 |
PriceCarey |
6.10 |
4.99 |
10.31 |
25.21 |
-15.23 |
|
2009 |
QuickJonathan |
1.30 |
-2.89 |
12.81 |
22.22 |
-28.00 |
|
2009 |
RaskTuukka |
24.10 |
26.92 |
10.02 |
46.57 |
7.27 |
|
2009 |
RaycroftAndrew |
2.00 |
1.18 |
5.92 |
12.78 |
-10.42 |
|
2009 |
RinnePekka |
4.70 |
2.33 |
11.23 |
24.35 |
-19.69 |
|
2009 |
RolosonDwayne |
0.00 |
-3.19 |
11.37 |
19.10 |
-25.48 |
|
2009 |
SalakAlexander |
-1.90 |
-2.03 |
1.87 |
1.64 |
-5.70 |
|
2009 |
SchneiderCory |
0.40 |
0.25 |
2.20 |
4.55 |
-4.05 |
|
2009 |
SmithMike |
-5.60 |
-10.64 |
9.76 |
8.50 |
-29.78 |
|
2009 |
TheodoreJose |
4.80 |
3.98 |
10.80 |
25.14 |
-17.18 |
|
2009 |
ThomasTim |
7.50 |
7.10 |
9.94 |
26.58 |
-12.38 |
|
2009 |
TokarskiDustin |
-1.20 |
-1.62 |
1.11 |
0.56 |
-3.80 |
|
2009 |
ToskalaVesa |
-16.90 |
-21.37 |
8.08 |
-5.54 |
-37.20 |
|
2009 |
TurcoMarty |
7.60 |
7.93 |
11.51 |
30.48 |
-14.62 |
|
2009 |
ValiquetteSteve |
-5.60 |
-7.05 |
3.28 |
-0.62 |
-13.48 |
|
2009 |
VarlamovSemyon |
2.30 |
0.08 |
7.70 |
15.16 |
-15.00 |
|
2009 |
VokounTomas |
29.30 |
32.15 |
13.14 |
57.90 |
6.40 |
|
2009 |
WardCam |
10.80 |
11.49 |
10.85 |
32.75 |
-9.77 |
|
2009 |
ZabaMatt |
-0.40 |
-0.38 |
1.22 |
2.00 |
-2.76 |
Appendix B
GGVT: GGVT from Tom’s tables
GVA: GVA calculated as before
GGVT*: GGVT calculated as before
Defference: GGVT – GVA
|
Year |
Name |
GGVT |
GVA |
GGVT* |
Difference |
|
2005 |
GerberMartin |
11.80 |
-10.40 |
-3.64 |
22.20 |
|
2005 |
KhabibulinNikolai |
-7.40 |
-26.29 |
-16.15 |
18.89 |
|
2005 |
GaronMathieu |
-2.20 |
-19.80 |
-10.31 |
17.60 |
|
2005 |
TheodoreJose |
-11.80 |
-28.17 |
-18.13 |
16.37 |
|
2005 |
GrahameJohn |
-9.60 |
-24.79 |
-14.91 |
15.19 |
|
2005 |
AuldAlex |
11.40 |
-3.41 |
2.55 |
14.81 |
|
2005 |
TurcoMarty |
5.10 |
-8.91 |
-2.35 |
14.01 |
|
2005 |
DipietroRick |
5.50 |
-8.37 |
-1.58 |
13.87 |
|
2006 |
ThomasTim |
8.70 |
-4.96 |
1.30 |
13.66 |
|
2005 |
DenisMarc |
5.70 |
-7.09 |
-1.35 |
12.79 |
|
2005 |
AebischerDavid |
2.60 |
-9.91 |
-3.61 |
12.51 |
|
2006 |
RaycroftAndrew |
-7.60 |
-20.08 |
-10.02 |
12.48 |
|
2005 |
MarkkanenJussi |
-9.80 |
-22.27 |
-14.42 |
12.47 |
|
2005 |
FleuryMarc-Andre |
3.60 |
-8.70 |
-2.60 |
12.30 |
|
2005 |
LuongoRoberto |
35.00 |
22.76 |
23.57 |
12.24 |
|
2005 |
NabokovEvgeni |
-10.60 |
-22.39 |
-13.78 |
11.79 |
|
2006 |
WardCam |
-3.00 |
-14.79 |
-6.95 |
11.79 |
|
2005 |
JosephCurtis |
9.20 |
-2.47 |
2.62 |
11.67 |
|
2006 |
BelfourEd |
4.60 |
-7.04 |
-1.30 |
11.64 |
|
2008 |
TurcoMarty |
-7.80 |
-19.33 |
-9.46 |
11.53 |
|
2005 |
KolzigOlie |
2.80 |
-8.43 |
-0.92 |
11.23 |
|
2006 |
FleuryMarc-Andre |
10.00 |
-1.22 |
4.10 |
11.22 |
|
2006 |
NiittymakiAntero |
-6.70 |
-17.90 |
-9.35 |
11.20 |
|
2005 |
BelfourEd |
-3.20 |
-14.38 |
-6.83 |
11.18 |
|
2005 |
NiittymakiAntero |
-0.70 |
-11.74 |
-5.47 |
11.04 |
|
2006 |
DenisMarc |
-16.10 |
-26.84 |
-17.47 |
10.74 |
|
2006 |
JosephCurtis |
-7.30 |
-17.90 |
-9.60 |
10.60 |
|
2005 |
RaycroftAndrew |
-10.40 |
-20.91 |
-13.57 |
10.51 |
|
2008 |
ToskalaVesa |
-16.10 |
-26.37 |
-15.95 |
10.27 |
