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Estimating Wins Using ERA and Run Support

Posted By Jeff Zimmerman On December 17, 2010 @ 9:08 am In Meta Analysis,Strategy | 7 Comments

Chasing wins in fantasy baseball sometimes seem futile, but if pursued in a logical way, they can be gained. Playing sub-par pitchers may increase win and strikeout totals, but they puts a drain on WHIP and ERA. By looking at the pitcher’s talent level and knowing the offense of the pitcher’s team, the chances of getting a win can be determined. The following are formulas to help estimate a pitchers win total.

First, all the qualified starters that didn’t switch teams from 2010 were matched with their team’s average runs scored per game. Then a linear regression was run comparing the player’s ERA, his run support and his actual winning percentage. The following equation was created:

Projected Winning % = 0.112(Run Support)-0.105(ERA)+0.446
with an R-squared = 0.827

With this equation, the expected number of wins can be estimated with just a couple more pieces of data. First, the number of starts that lead to a decision (win or loss) for games in 2010 was 70% with the bullpen getting the rest. Second, the number of GS will have to guesstimated using playing time projections and injury history. With this information, a projected number of wins can be calculated:

Projected Wins = 0.7 * Games Started * Projected Winning %

Going back over the 2010 numbers, the average difference between the number of games won and the predicted number of games won was 1.89 with a standard deviation was 2.24 wins.

For example, here is how Felix Hernandez’s win total would compare if he pitched for different teams during 2010. He was able to get 13 wins with a 2.47 ERA in 34 games with a team that average scoring 3.13 runs a game. With those numbers, he was projected to win 13.3 games. Now if he played for the Yankees and got their run support (5.23), his wins would have been around 18.9. If he had only got just 4.0 runs of support, he would have been closer to 15.6 wins.

Normally, trying to accumulate wins is a tough proposition. With a little knowledge of the pitcher and his team’s offense, the amount of wins the pitcher gets can be somewhat predicted.


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