Another wonderful (regular) season has come to a close. Mike Trout got better, again. Christian Yelich lost his mind, Jacob deGrom provided more value in one season than Clayton Kershaw ever has, and the Boston Red Sox set a franchise record for wins in a season. Throughout the season we have released Power Rankings based on a metric I created called weighted Run Differential or wRD for short. If you are unfamiliar with wRD, you can read how it's calculated HERE. In the last power rankings, the Houston Astros were the top team in baseball according to wRD Win %. In fact, the Astros have topped the Red Sox as baseball's best team throughout the season according to wRD. The season has ended and the same rule applies. It is no surprise this is the case. The Astros have a run differential of +263, 34 runs greater than the Red Sox +229. This was another wonderful 162 game season, that actually needs a few game 163's to sort everything out.
Now that the season is officially over, let's check out the final wRD Win % rankings!
The Houston Astros being projected to win 111 games is scary to me, and they should probably be the favorite to win the World Series, again. The biggest surprise to me is the Dodgers now rank second, ahead of the 108 win Red Sox. That could potentially expose some of the flaws of this rankings system, but I think there is some truth to these rankings. The Dodgers undoubtedly have underachieved a little this year, but their roster is extremely talented and they do rank third in baseball with a +191 run differential. Maybe the Dodgers are that much better than their record indicates. There is something oddly satisfying to me that after 162 games, the Cubs and Brewers are tied atop the NL Central standings and in terms of wRD Win %.
Those are the final power rankings for the 2018 season! If your team is ranked higher than their on field W-L record would indicate, this could be a boost of confidence for you going into 2019 or October. If the opposite is true, there is certainly room for error in a ranking system like this, but there could be some truth to your team's on field play. Luck and other variables play a role in wins and losses that the casual fan tends to overlook. With that being said, it's time to check out wRD predictive power! The following graphs look at how effective a team's performance through the first power rankings we released in July did at predicting their second half record. Win %, Pythagorean Win %, and wRD Win % will all be compared to second half win % to see which was the best predictor in this test.
Pythagorean Win % did the best job at predicting future record than wRD Win % and Win %. Although wRD Win % performed better than overall Win %, the goal of these rankings were to create a system that performed better than Pythagorean Win %. By this measure, I did not achieve this feat. Of course, there are more ways to measure this and potentially much larger sample sizes to perform tests on, which I will look into in the future.
In the future, I look forward to running more tests evaluating wRD win %. For now, that is all for the 2018 regular season! Tomorrow we will be releasing an article that looks at World Series odds using wRD Win % numbers. I hope you all enjoyed this segment of SOTG, I had a ton of fun creating these rankings, and I look forward to creating more metrics in the future! If anyone would like the spreadsheets I created to formulate these rankings, please reach out to studentsofbaseball@gmail.com !