The Accuracy of Component ERA

by Cyril Morong

Click here to see my sabermetric blog called Cybermetrics

(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