The Baseball Gauge Glossary
Postseason Series Win Expectancy
Series win expectancy shows a team's probability of winning a postseason series based on factors such as series record, score, inning, outs, base runners, and run scoring environment. It is a way to tell the story of the series and to show how each play impacted the outcome. This takes individual game win expectancy and places it into the bigger picture of the postseason series.
Home Field Advantage
Most individual game win expectancy graphs do not give an advantage to the home team, thus giving each team a 50% chance of victory at the beginning of a game. Due to the emphasis placed on earning home field advantage for the series, a home field advantage in the calculations. The actual figure used is based on the home team's winning percentage from all games over a five-year period. For example, a home team in a 1988 game would be given a 54.41% chance of winning since that his the home team's winning percentage in all games from 1986-1990.
The overall series win expectancy is determined by simulating the remaining games 100 million times. For example, at the beginning of a 7-game series in 1988 with a 2-3-2 format, the team with the home field advantage for the series would be the winner of these simulations 51,384,236 times, or a 51.4% win expectancy.
If the home team were to win game 1, their series win expectancy would increase to 65.7%. If they were to lose game 1, their series win expectancy would decrease to 34.3%. This means that the individual game win expectancy graph for game 1 would begin at 51.4% and either end at 65.7% or 34.3%.
Win expectancy can fluctuate with any change in the score, inning, out(s), and/or base runners. Because of this, each play has a series win expectancy change value. This is simply a team's series win expectancy at the end of the play minus its series win expectancy at the beginning of the play.
World Series Win Expectancy
World Series win expectancy is the probability that a team will win the World Series. This is calculated by dividing the series win expectancy by the number of rounds a team is away from the World Series, plus 1.
WE = Series win expectancy
x = Number of rounds away from World Series
World Series WE = WE / (x + 1)
Francisco Cabrera's game winning 2-run single in the Seventh Game of the 1992 NLCS had a 74% series win expectancy change. The Braves win expectancy was 26% at the beginning of the play, and it increased to 100% at the end. Since the NLCS is one round away from the World Series, we divide this value by 2 to get the World Series win expectancy value.
World Series WE = 74% / (1 + 1) = 37%
In other words, this play increased the Braves chance of winning the World Series by 37 percentage points.
This is simply the losing team's highest series win expectancy during the series.
aCLI / aLI
Average (Championship) Leverage Index over the course of the series or game
Avg cWPA / Avg WPA
Average change in (Championship) Win Probability Added over the course of the series or game
Total cWPA / Total WPA
Cumulative change in (Championship) Win Probability Added over the course of the series or game