Posted by Sean Forman on March 26, 2010
This is the fourth of ten features we are adding for our 10th anniversary.
The first place I saw Win Expectancy (WE) was when I was writing for the Big Baseball Annual back in the late 1990's. Doug Drinen, who has since moved on to become one of the leading NFL analysts and creator of Pro-Football-Reference.com, wrote a series of articles on reliever usage that built on the original Mills Brothers work on Win Expectancy (WE). Doug even included a WS Game WE Graph in one of the books. I always have thought it was an elegant measurement of what happened during the game and I'm excited to now have it on the site.
Tom Tango was very helpful in working out the details for implementation. His run environment adjusted numbers for Win Expectancy, Leverage, Base-Out Run Expectancy and Base-Out Leverage are the basis for the numbers you see on the site.
A quick rundown of what is on the site. WE and RE appear for seasons for which we have play-by-play, 1952-2009. The data is only 100% complete for 1974-present. For the earlier seasons, we are missing some games for each season. A full listing of our coverage is here.
- The More Stats sections for pitchers and hitters have tables with Win Expectancy, Run Expectancy and Pitching and Batting Runs and Wins (Jack Morris / Mike Schmidt). This chart has four wins-based metrics, batting or pitching Wins, WPA, WPA/LI, and REW.
- All Regular Season Box Scores for which we have PBP have interactive WE Charts. (Tigers @ Twins Playoff Game / Tutorial Video highlighting the features on the chart)
- These stats also now appear on player gamelog pages.
- Team Detailed/More Stats (link just above the team batting stats) pages have full team Win Probability, RE24, and Batting and Pitching Wins statistics. (1979 Pirates Batting / 2001 D'Backs Pitching)
- 1952-Present League Pages have complete RE and WE registers. Select Win Probability from the list of options in the nav bar just above the league batting stats. (2007 NL Pitching / 1980 MLB Batting)
- Leaderboards for these stats have been added to yearly league pages (2009 NL Pitching), team all-time leaderboards (Mets Batting Leaders), and the leaders section (All-Time Pitching Wins / Year-by-Year Pitching REW).
- I've created a full (perhaps even tedious) rundown of the method used to create these stats and the specific stats provided. Please let me know if you have any questions or complaints.
- This data is integrated with the Play Index, so you can now find things like:
- Greatest Amount of WPA by Reliever from 1980-2009
- Greatest RE24 for a Second Baseman in a season since 1952
- Longest Streak of High Leverage (aLI > 2.00) for a Pitcher
- Most Games in a season in the last decade with RE24 ≤ 0
- Highest WPA games of 2009 for hitters
- Highest Seasonal WPA with REW ≤ 0.00 for a Pitcher
I hope you are enjoying these improvements to the site as much as I'm enjoying putting them together. Be sure to three earlier features as well. Questions and comments are always welcome. I'm hoping update #5 will come next week, but given the onrushing advance of Opening Day it may occur after first pitch.
ERA+ update: yesterday, I mentioned that we erroneously changed the definition for ERA+. I am still considering a long-term change, but for the short-term have changed it back. I apologize for the confusion.