The Accuracy of Component ERA

 

by Cyril Morong

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(Note-I added new information below on June 17, 2005. Using regression analysis, I made an improvement in the model. This is explained at the end of the article.)

 

Please let me know if someone has done this already. I looked at the 70 pitchers who pitched at least 3000 innings between 1920 and 2000. The correlation between their actual ERA and the Component ERA that Bill James invented is .918. So the r-squared would be .843, meaning that 84.3% of the variation in ERA across pitchers could be explained by their component ERA.

 

The formula is complicated.  It uses a pitcher’s number of batters faced, hits allowed, HRs allowed, walks allowed, and HBP. It can be found at

 

http://www.uri.edu/personal/jkuh9192/conc.html

 

 (I can't tell whose site this is)

 

Only 8 of the 70 pitchers had a CERA that was more than .25 different from their actual ERA. Even if a pitcher pitched 40 complete games in a season, a differential here of .25 or less means less than 10 runs in a season, or about 1 win.

 

One interesting thing is that only 18 pitchers had lower CERAs than their actual. So 52 had higher CERAs than their actual. It seems like it should be close to half for each. I have not tried to figure out how it could be made better. The average differential is .066 (including negatives). The average absolute differential is .116.

 

The table below shows the results.  First their actual ERA, then CERA, the differential. If anyone has any theories as to why these pitchers are the best, I would be happy to hear them. I listed the most negative values first, indicating the pitchers who went the most below their CERAs.

 

 

Pitcher

ERA

CERA

Diff

Tom Zachary

3.74

4.01

-0.271

Whitey Ford

2.74

2.97

-0.225

Mike Torrez

3.96

4.15

-0.188

Claude Osteen

3.30

3.44

-0.141

Tommy John

3.34

3.48

-0.138

Murry Dickson

3.66

3.79

-0.135

Phil Niekro

3.35

3.46

-0.109

Larry French

3.44

3.55

-0.106

Jim Kaat

3.45

3.54

-0.087

Lefty Grove

3.06

3.12

-0.061

Bucky Walters

3.30

3.36

-0.057

Jim Palmer

2.86

2.91

-0.054

Jesse Haines

3.65

3.69

-0.045

Rick Reuschel

3.37

3.41

-0.037

Mel Harder

3.80

3.83

-0.028

Joe Niekro

3.59

3.61

-0.017

Jim Perry

3.45

3.46

-0.015

Don Drysdale

2.95

2.96

-0.012

Bob Welch

3.47

3.47

-0.003

Bob Friend

3.58

3.58

0.003

Frank Tanana

3.66

3.65

0.007

Curt Simmons

3.54

3.53

0.013

Steve Carlton

3.22

3.2

0.015

Dutch Leonard

3.25

3.22

0.028

Jerry Koosman

3.36

3.33

0.029

Billy Pierce

3.27

3.24

0.030

Jerry Reuss

3.64

3.6

0.037

Freddie Fitzsimmons

3.51

3.47

0.038

Milt Pappas

3.40

3.36

0.038

Bobo Newsom

3.98

3.94

0.043

Bob Gibson

2.91

2.86

0.054

Warren Spahn

3.09

3.03

0.055

Dolf Luque

3.25

3.19

0.058

Ted Lyons

3.67

3.61

0.058

Orel Hershiser

3.25

3.19

0.060

Early Wynn

3.54

3.48

0.060

Bob Feller

3.25

3.19

0.064

Burleigh Grimes

3.65

3.58

0.067

Doyle Alexander

3.76

3.69

0.068

Earl Whitehill

4.36

4.29

0.070

Jim Bunning

3.27

3.2

0.070

Bert Blyleven

3.31

3.23

0.084

Rick Wise

3.69

3.6

0.087

Waite Hoyt

3.60

3.51

0.088

Larry Jackson

3.40

3.31

0.092

Charlie Hough

3.75

3.65

0.096

Mickey Lolich

3.44

3.34

0.097

Carl Hubbell

2.98

2.88

0.097

Gaylord Perry

3.11

3

0.105

Dennis Martinez

3.68

3.56

0.120

Lew Burdette

3.66

3.53

0.126

Vida Blue

3.26

3.13

0.130

Luis Tiant

3.30

3.16

0.144

Paul Derringer

3.46

3.31

0.148

Charlie Root

3.59

3.43

0.156

Juan Marichal

2.89

2.73

0.160

Tom Seaver

2.86

2.67

0.192

Roger Clemens

3.07

2.88

0.193

Robin Roberts

3.40

3.21

0.195

Greg Maddux

2.83

2.63

0.197

Sam Jones

3.94

3.74

0.201

Danny Darwin

3.75

3.54

0.210

Eppa Rixey

3.34

3.12

0.220

Jack Morris

3.90

3.61

0.290

Ferguson Jenkins

3.34

3.04

0.298

Nolan Ryan

3.19

2.89

0.303

Catfish Hunter

3.26

2.94

0.317

Red Ruffing

3.80

3.48

0.319

Dennis Eckersley

3.49

3.11

0.380

Don Sutton

3.26

2.88

0.381

 

Source: The STATS, INC. All-Time Major League Handbook, their 2001 Major League Handbook and Lee Sinins Sabermetric Encyclopedia.

 

 

New Information

 

Bob Clark of Louisville suggested that I take lefties into account in looking at component ERA (ERC). The big reason to me might be that lefties face more right handed batters so they might get more GIDPs. So they might have lower ERAs than projected based on hits, BBs, and HRs than RHPs. Also, the more strikeouts a pitcher has, the fewer GIDPs he will probably have. That might increase runs allowed.

 

So I ran a regression in which the dependent variable was ERA and the independent variables are ERC, strikeouts per IP and a dummy variable for being a lefthanded pitcher (1 if yes, 0 if no). The regression equation was

 

ERA = .427 + .881*CERA + .1188*SO/IP - .0986*DUM

 

Dum had a t-value of about -3. The r-squared was .866 and the standard error was .116. The formula predicts all pitchers to within .299 or less. 63 were off by less than .2 and 48 were within .1. The average difference between the predicted value and the actual ERA is basically zero (.0006 again), probably because the over and under predictions cancel out. The average absolute deviation was .062. 36 were over predicted and 34 were underpredicted. ERC by itself underpredicted 51 of the 70. So adding in the dummy variable made things just a little more accurate than the ERC + strikeouts model.

 

 I used all pitchers with 3000+ IP from 1920-2000. 

 

I also tried the regression with interaction or slope terms for the dummy variable. The results were similar.

 

Below are the results. The Predicted ERA is the one predicted by the equation above.

 

 

Pitcher

ERA

CERA

Predicted ERA

Diff

Whitey Ford

2.74

2.97

3.018

-0.278

Phil Niekro

3.35

3.46

3.549

-0.199

Jim Palmer

2.86

2.91

3.057

-0.197

Mike Torrez

3.96

4.15

4.138

-0.178

Don Drysdale

2.95

2.96

3.121

-0.171

Murry Dickson

3.66

3.79

3.816

-0.156

Tom Zachary

3.74

4.01

3.889

-0.149

Bob Gibson

2.91

2.86

3.042

-0.132

Bucky Walters

3.30

3.36

3.430

-0.130

Rick Reuschel

3.37

3.41

3.499

-0.129

Claude Osteen

3.30

3.44

3.414

-0.114

Tommy John

3.34

3.48

3.451

-0.111

Bob Welch

3.47

3.47

3.560

-0.090

Lefty Grove

3.06

3.12

3.145

-0.085

Jim Perry

3.45

3.46

3.532

-0.082

Joe Niekro

3.59

3.61

3.665

-0.075

Bob Feller

3.25

3.19

3.317

-0.067

Jim Bunning

3.27

3.20

3.336

-0.066

Jesse Haines

3.65

3.69

3.714

-0.064

Orel Hershiser

3.25

3.19

3.314

-0.064

Jim Kaat

3.45

3.54

3.512

-0.062

Larry French

3.44

3.55

3.501

-0.061

Bob Friend

3.58

3.58

3.638

-0.058

Dutch Leonard

3.25

3.22

3.307

-0.057

Milt Pappas

3.40

3.36

3.452

-0.052

Bert Blyleven

3.31

3.23

3.361

-0.051

Mel Harder

3.80

3.83

3.841

-0.041

Gaylord Perry

3.11

3.00

3.148

-0.038

Dolf Luque

3.25

3.19

3.279

-0.029

Steve Carlton

3.22

3.20

3.242

-0.022

Juan Marichal

2.89

2.73

2.910

-0.020

Early Wynn

3.54

3.48

3.554

-0.014

Tom Seaver

2.86

2.67

2.870

-0.010

Roger Clemens

3.07

2.88

3.078

-0.008

Freddie Fitzsimmons

3.51

3.47

3.516

-0.006

Larry Jackson

3.40

3.31

3.405

-0.005

Greg Maddux

2.83

2.63

2.828

0.002

Luis Tiant

3.30

3.16

3.293

0.007

Billy Pierce

3.27

3.24

3.255

0.015

Bobo Newsom

3.98

3.94

3.964

0.016

Jerry Koosman

3.36

3.33

3.341

0.019

Burleigh Grimes

3.65

3.58

3.623

0.027

Doyle Alexander

3.76

3.69

3.732

0.028

Rick Wise

3.69

3.60

3.661

0.029

Ted Lyons

3.67

3.61

3.638

0.032

Charlie Hough

3.75

3.65

3.716

0.034

Warren Spahn

3.09

3.03

3.056

0.034

Frank Tanana

3.66

3.65

3.623

0.037

Curt Simmons

3.54

3.53

3.499

0.041

Waite Hoyt

3.60

3.51

3.558

0.042

Dennis Martinez

3.68

3.56

3.627

0.053

Carl Hubbell

2.98

2.88

2.921

0.059

Paul Derringer

3.46

3.31

3.392

0.068

Mickey Lolich

3.44

3.34

3.363

0.077

Jerry Reuss

3.64

3.60

3.562

0.078

Lew Burdette

3.66

3.53

3.579

0.081

Robin Roberts

3.40

3.21

3.315

0.085

Charlie Root

3.59

3.43

3.503

0.087

Nolan Ryan

3.19

2.89

3.099

0.091

Vida Blue

3.26

3.13

3.163

0.097

Danny Darwin

3.75

3.54

3.622

0.128

Ferguson Jenkins

3.34

3.04

3.189

0.151

Catfish Hunter

3.26

2.94

3.086

0.174

Sam Jones

3.94

3.74

3.760

0.180

Earl Whitehill

4.36

4.29

4.153

0.207

Don Sutton

3.26

2.88

3.045

0.215

Jack Morris

3.90

3.61

3.684

0.216

Eppa Rixey

3.34

3.12

3.106

0.234

Dennis Eckersley

3.49

3.11

3.254

0.236

Red Ruffing

3.80

3.48

3.547

0.253

 


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