Comparing GGVT to GVA

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

 

 

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