The Baseball Gauge Glossary
For every day of every season, the remaining schedules are simulated 100,000 times. In these simulations, all teams are considered equal except for that the home team gets a home field advantage. This home field advantage is the record for all home team's from five years before and five years after the current season.
For example, when simulating the 1978 season, the home field advantage used is 53.96%. This was the winning percentage for all home team's from 1973-1983.
For the strike shortened years of 1981 (first half) and 1994, the original schedules were simulated. This is why no team finishes with 100% during those seasons.
100,000 simulations of the remaining schedules from every day in Major League Baseball history is no easy task. There were roughly 1.8 trillion games simulated from 1871-2014.
Pennant Win Expectancy
The simulations give us different probabilities for different eras in baseball history
For seasons prior to 1969: League championship Expectancy
For seasons from 1970 to 1993: Division championship Expectancy
For seasons from 1994 to 2011: Division and Wild Card Expectancies (where Division + Wild Card = Playoff Expectancy)
For seasons from 2012 to present: Division and Wild Card Expectancies (where Division + Wild Card / 2 = Playoff Expectancy)
World Series Win Expectancy
The addition of playoff teams and rounds over the course of baseball history requires us to change the calculations for World Series win expectancy. This is calculated by dividing the division or league pennant win expectancy by the number of postseason teams that year.
For seasons prior to 1969: League / 2
For seasons from 1970 to 1993: Division / 4
For seasons from 1994 to 2011: (Division + Wild Card) / 8
For seasons from 2012 to present: (Division + Wild Card / 2) / 8