Win Probability Changes

You may have noticed the Win Probability numbers have changed slightly. Don’t panic! There have been a few changes, for the better.

First off, we’re now using Tangotiger’s updated win expectancy tables which are no longer a flat 5.0 Runs per Game environment. Instead, we’re using the home team’s league, average run environment. This now puts batters and pitchers on “equal footing” and you should now be able to accurately compare batters and pitchers using WPA.

Second of all, we’re also using Tangotiger’s run expectancy tables to calculate Batting Runs Above Average (BRAA) for both batters and pitchers. Once again the run environment is set at the home team’s league, average run environment.

Next to BRAA there is a column titled “REW”, which stands for Run Expectancy Wins. This is a replacement for OPS Wins because we no longer need to estimate wins in a context neutral environment since we’re now using run expectancy.

Finally, Clutchiness has been shortened to Clutch (Clutchiness was excessively long) and is calculated as WPA/LI – REW.

Update (3/4/2007): Clutch has been switched back to being calculated with OPS Wins. More on this later.

Typically players remain in the same order, but their values have changed slightly. Batters should be slightly more valuable and pitchers slightly less valuable based on WPA scores.

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David Appelman is the creator of FanGraphs.

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