## Tuesday, October 28, 2014

### The Relationship Between OPS Differential And Winning Percentage Using 5 Year Averages

See a recent post called The Relationship Between Team OPS Differential And Winning Percentage, By Decades. I used regression analysis to see how big the impact of OPS differential was on winning.

Here, instead of using individual years, I used the average OPS differential and average winning pct for all 30 teams over the last 5 years.

The regression equation from using individual years was

Pct = 1.325*OPSDIFF + .5

The r-squared was .827 and the standard error was .029. Over 162 games, that is 4.639 wins

The regression equation from using the 5 year average was

Pct = 1.3465*OPSDIFF + .5

The r-squared was .869 and the standard error was .017. Over 162 games, that is 2.72 wins. That is a big drop from the first regression. In a given year, luck will play a role. But the more seasons and data that are used the more accurate the relationship. By combining the years, some of the good and bad luck evens out.

The table below shows the prediction for each team. It seems strange the 6 most extreme teams are all pretty far from the rest of the pack. The Orioles were predicted to have a .476 pct but it was actually .505. That means they won 4.762 more games per season than their OPS differential would estimate.

 Team OPSDIFF W-L% Pred Diff Per 162 BAL -0.018 0.505 0.476 0.029 4.762 PHI -0.001 0.526 0.498 0.028 4.532 NYY 0.026 0.563 0.535 0.028 4.473 ATL 0.027 0.554 0.536 0.018 2.949 CLE -0.021 0.487 0.472 0.014 2.349 MIN -0.053 0.443 0.429 0.014 2.266 SFG 0.018 0.538 0.525 0.013 2.157 CIN 0.017 0.535 0.523 0.012 1.912 SDP -0.023 0.481 0.470 0.012 1.899 PIT -0.018 0.481 0.476 0.006 0.939 NYM -0.024 0.473 0.467 0.006 0.931 KCR -0.023 0.475 0.470 0.006 0.894 ARI -0.020 0.475 0.473 0.002 0.371 STL 0.041 0.557 0.555 0.002 0.360 TOR -0.009 0.489 0.487 0.002 0.251 LAA 0.023 0.532 0.531 0.001 0.149 WSN 0.024 0.530 0.533 -0.003 -0.415 SEA -0.037 0.446 0.450 -0.004 -0.640 TBR 0.040 0.550 0.554 -0.004 -0.687 LAD 0.030 0.536 0.541 -0.004 -0.709 OAK 0.029 0.535 0.539 -0.005 -0.738 TEX 0.035 0.539 0.547 -0.008 -1.247 CHW -0.008 0.479 0.489 -0.010 -1.642 MIL 0.016 0.509 0.522 -0.013 -2.115 HOU -0.078 0.380 0.395 -0.015 -2.379 DET 0.050 0.552 0.567 -0.015 -2.446 FLA -0.029 0.444 0.461 -0.016 -2.612 CHC -0.032 0.427 0.458 -0.030 -4.918 BOS 0.034 0.514 0.546 -0.032 -5.231 COL -0.017 0.444 0.478 -0.033 -5.404

Here is a graph of the relationship