The Relationship Between Team OPS Differential And Winning Percentage, By Decades

I learned on Oct 21 that there are some discrepancies between Baseball Reference and Retrosheet, so I can't be sure of these results. If I learn more, I will report it.


Oct 24. Here are the corrected numbers:

Period	DIFF	INT	r squared	Std error	Per 162 Games
1914-19	1.866	0.498	0.833	0.038	6.207
1920-29	1.375	0.500	0.866	0.033	5.390
1930-39	1.442	0.500	0.851	0.038	6.157
1940-49	1.515	0.500	0.854	0.036	5.754
1950-59	1.452	0.500	0.874	0.032	5.165
1960-69	1.458	0.500	0.816	0.035	5.590
1970-79	1.361	0.500	0.811	0.032	5.165
1980-89	1.352	0.500	0.745	0.033	5.399
1990-99	1.249	0.500	0.780	0.032	5.109
2000-09	1.293	0.500	0.809	0.032	5.120
2010-14	1.325	0.500	0.827	0.029	4.639

Data from the Baseball Reference Play Index and Retrosheet.

DIFF is the value of the coefficient on OPS differential in the regression. INT is the intercept. Std error is the standard error. Per 162 games is the standard error times 162.

It seems like the relationship has gotten slightly stronger over time if you look at the standard errors, although the DIFF coefficient does not seem to be as strong as it used to be.

Also, for some reason, before the 1960s, the intercept was below .500. You might expect a team with a .000 OPS differential to have a .500 record. But that was not the case for some time. Not sure why. Maybe greater imbalance in talent levels across teams (like those great Yankee teams) meant that if you were just "average" you lost alot more than you would expect when you played those top teams.

Period	DIFF	INT	r squared	Std error	Per 162 Games
1914-19	1.898	0.429	0.802	0.042	6.759
1920-29	1.366	0.441	0.803	0.040	6.542
1930-39	1.548	0.423	0.822	0.042	6.807
1940-49	1.537	0.467	0.794	0.042	6.837
1950-59	1.486	0.494	0.858	0.034	5.490
1960-69	1.458	0.500	0.816	0.035	5.590
1970-79	1.361	0.500	0.811	0.032	5.165
1980-89	1.352	0.500	0.745	0.033	5.399
1990-99	1.249	0.500	0.780	0.032	5.109
2000-09	1.293	0.500	0.809	0.032	5.120
2010-14	1.325	0.500	0.827	0.029	4.639