In 2016, I dusted off Bill James’s “World Series Prediction System,” which James developed in 1972 and introduced to a wider audience in Inside Sports in 1982 and the 1984 Bill James Baseball Abstract. The system from the 1984 Abstract was:

• Give the team with the better record one point for each half-game difference in won-lost percentage.
• Give three points to the team that scored the most runs.
• Give 14 points to the team that hit fewer doubles.
• Give 12 points to the team that hit more triples.
• Give 10 points to the team that hit more home runs.
• Give 8 points to the team with the lower batting average.
• Give 8 points to the team with fewer errors.
• Give 7 points to the team that had more double plays.
• Give 7 points to the team that allowed more walks.
• Give 19 points to the team that threw more shutouts.
• Give 15 points to the team whose ERA was more below the league average.
• Give 12 points to the team with most recent postseason experience. (In case of a tie, give the points to the team that had greater success.)
• For intraleague series, give 12 points to the team with the better head-to-head record.

He calculated the weights by considering every postseason series and checking how often the winning team exhibited certain characteristics. Shutouts got a weight of 19 because among the series he considered, the team with more shutouts won 19 more times than it lost. The team with the fewer doubles won 14 more times, the team with the lower relative ERA won 15 more times, etc. And there’s an element of intuitive sense; high-average offenses may be dependent on stringing a lot of singles and doubles together, while scoring in the postseason is often longball-dependent.

I updated the system in 2016. James didn’t have data from 31 World Series and 62 Championship Series that I had that year. And the Division Series didn’t even exist until 1995. I found two significant changes by compiling the data since the 1984 Abstract. First, unsurprisingly, the weights have changed. Second, I found that the weights differed depending on the type of series (Division vs. Championship vs. World). So I developed different formulae for each series type. I’ve updated it annually. For the World Series, I’ve considered only those played since 1969. I have omitted the 1981, 1994, and 2020 seasons.

And now, with one more World Series, two more Championship Series, and four more Division Series under our belts, I was able to update the weights further. (I should note that somewhere along the line, someone suggested I change the variables into more modern ones. I haven’t forgotten this. I haven’t done it, either.)

Here are the formulae for the 2026 postseason, using James’ original framework.