Measuring the Accuracy of Baseball's Win-Percentage Estimators

Analyst Written on September 06, 2008

(Page 2 of 2)

Team	Wins	Exp.Wins	Diff.
Atlanta	62	68.5	6.5
Cleveland	68	73.9	5.9
Toronto	75	80.0	5.0
San Diego	54	58.0	4.0
Seattle	55	58.9	3.9
Philadelphia	77	80.3	3.3
Baltimore	63	65.7	2.7
Boston	83	85.7	2.7
Chicago Cubs	85	87.7	2.7
Oakland	64	66.5	2.5
Detroit	67	68.7	1.7
LA Dodgers	71	72.6	1.6
Arizona	71	72.0	1.0
Washington	54	54.7	0.7
Chicago Sox	79	79.6	0.6
St. Louis	75	75.4	0.4
Minnesota	78	78.3	0.3
NY Mets	79	79.1	0.1
NY Yankees	75	74.7	-0.3
Cincinnati	63	61.4	-1.6
Colorado	67	65.4	-1.6
Milwaukee	81	78.5	-2.5
Pittsburgh	60	57.4	-2.6
San Francisco	60	57.2	-2.8
Kansas City	60	57.1	-2.9
Florida	72	67.6	-4.4
Texas	69	64.4	-4.6
Tampa Bay	85	79.1	-5.9
Houston	74	67.7	-6.3
LA Angels	85	75.8	-9.2

Because the Angels have won so many close games, their closer gets more save opportunities, and they have won more games than expected. Tampa Bay is also at the bottom for "lucky" teams—and guess what, the Blue Jays should have more wins than them!

—————————————————————————————————————————————

Differential formulas

W% = X * (R - RA) / G + .5

Where X is for different methods...

Palmer-RPW: 1 / (10 * sqrt(runs per inning))

Tango-RPW: 1 / (RPG / 2 + 5), where RPG = (runs allowed + runs scored)/(games played)

RPW=10 : 0.1

RPW=RPG : 1 / RPG

~~~

Ratio formulas:

W% = (RS^x)/(RS^x + RA^x)

Where x is for different methods...

Pythagenport: 1.5 * log(RPG) + .45

Pythagenpat: RPG^.287

Pythag-1.83: 1.83

Pythag-2: 2

~~~

Others

Ben V-L: W% = 0.91 * (RS-RA) / (RS+RA) + .5

Soolman: W% = (0.102 * RS - 0.103 * RA) / G + .505

E.Cook: W% = 0.484 * RS / RA

Double Edge: W% = (RS / RA * 2 - 1) / (RS / RA * 2)

Kross: For teams with RS>RA, W% = RS / (2 * RA) , and for teams with RA>RS, W% = 1 - RA / (2 * RS) . I used the first formula for teams with an equal number of runs scored and runs allowed.

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