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Cameron: FanGraphs and Baseball-Reference.com are unifying 'replacement level'

From Dave Cameron at FanGraphs on March 28, 2013:

On Christmas Eve of 2008, David Appelman gave the world a present – “win values” on the pages of FanGraphs. It wasn’t labeled WAR for a little while longer, though it was an implementation of the model Tom Tango laid out at The Book Blog a few months prior. Over these last four years, the model has become quite popular, and even those who are not fans of analytics know what WAR stands for. Over time, the model grew in popularity, and in 2010, Baseball Reference added it to their collection of statistics. Because WAR is essentially a model of player value, there are decisions that have to be made about the way it is constructed that don’t have an obviously correct answer. In places where we had made one decision, Sean Forman (and Sean Smith, who assisted with their original implementation) made some other decisions, and the calculations differ in some significant ways.

We know that this is a source of frustration for some folks, having two sites both publicly display different calculations for a statistic of the same name. Often, the differences between the two have been used to discredit the entire model.

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Even with very different inputs, both models came to the same conclusion about [Jack] Morris – he was a slightly above average pitcher who had a very long career. So, why did we give him credit for an additional 17.6 wins? The answer, quite simply, lies with replacement level. Our model used a lower baseline than Baseball-Reference did, so the same performance would result in a higher WAR in our model than in theirs.

Read the full article here: http://www.fangraphs.com/blogs/index.php/unifying-replacement-level/

This page was last updated March 28, 2013 at 12:51 pm MST.

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