Flu-Like Symptoms: The Bill James World Series Prediction System, 2019 Edition

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
• 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
• 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.

And now, with one more World Series, two more Champion ship Series, and four more Division Series under our belts, I was able to update the weights further. Here are the formulae for the 2019 postseason, using James’ original framework.

DIVISION SERIES

• Give 14 points to the team with fewer doubles
• Give 17 points to the team with fewer triples
• Give 8 points to the team with the most home runs
• Give 8 points to the team whose batters had fewer walks
• Give 15 points to the team whose batters had fewer strikeouts
• Give 8 points to the team that had a higher on base percentage
• Give 6 points to the team that had a lower slugging percentage
• Give 8 points to the team that had fewer errors
• Give 10 points to the team with the lower ERA
• Give 28 points to the team that pitched more shutouts
• Give 10 points to the team whose pitchers had more strikeouts
• Give 14 points to the team with more recent postseason experience

CHAMPIONSHIP SERIES

• Give 14 points to the team that scored more runs
• Give 12 points to the team that hit fewer triples
• Give 13 points to the team that hit more home runs
• Give 14 points to the team with the higher batting average
• Give 12 points to the team with the higher on base percentage
• Give 12 points to the team with the higher slugging percentage
• Give 11 points to team that turned fewer double plays
• Give 8 points to the team whose pitchers had fewer strikeouts
• Give 6 points to the team whose pitchers allowed fewer walks
• Give 8 points to the team with the lower ERA
• Give 16 points to the team with better record
• Give 6 points to the team with better head-to-head record

WORLD SERIES

• Give 12 points to the team that scored more runs
• Give 6 points to the team that hit more doubles
• Give 10 points to the team that hit more triples
• Give 6 points to the team with the higher batting average
• Give 6 points to the team with the higher slugging percentage
• Give 10 points to team whose pitchers had more strikeouts
• Give 18 points to the team whose pitchers allowed more walks
• Give 11 points to the team with the more recent postseason experience

And the weights worked pretty well. Looking at all postseason series since 1969, the year divisional play (and the Championship Series) began, the formulae above correctly predicted 70.8 percent of Division Series, 63.7 percent of Championship Series, and 70.2 percent of World Series. Last year it got every postseason series correct,

As an example, let’s break down one of the surprising first-round selections, 91-71 St. Louis over 97-65 Atlanta.

• Louis had 31 fewer doubles. Fourteen points for the Cardinals.
• Louis had 5 fewer triples. Seventeen points for the Cardinals.
• Atlanta had 39 more homers. Eight points for the Braves.
• Louis had 58 fewer walks. Eight points for the Cardinals.
• Louis had 47 fewer strikeouts. Fifteen points for the Cardinals.
• Atlanta’s OBP was 14 points higher. Eight points for the Braves.
• Louis’s SLG was 37 points lower. Six points for the Cardinals.
• Louis committed 12 fewer errors. Eight points for the Cardinals.
• Louis’s ERA was 0.39 lower. Ten points for the Cardinals.
• Louis’s pitchers threw six more shutouts. Twenty-eight points for the Cardinals.
• Louis struck out six more batters. Ten points for the Cardinals.
• Atlanta has more recent postseason experience. Fourteen points for the Braves.

That’s 116 for the Cardinals, 30 for the Braves. Hey, don’t @ me. I’m just reporting here.

So what do they say for this year? I’ll give you every possible outcome.

DIVISION SERIES

Yankees over Twins
Astros over Rays
Cardinals over Braves
Dodgers over Nationals

CHAMPIONSHIP SERIES

Astros over all American League opponents
Yankees over Rays
Twins over Rays
Dodgers over all National League opponents
Nationals over Braves
Nationals over Cardinals

WORLD SERIES

Yankees over all National League teams
Astros over all National League teams
Braves over Rays
Nationals over Rays
Rays over Cardinals
Dodgers over Rays
Twins over Braves
Nationals over Twins
Twins over Cardinals
Twins over Dodgers

So, per the system, the most likely outcomes are:

DIVISION SERIES: Dodgers and Cardinals advance in National League, Astros and Yankees advance in American League
CHAMPIONSHIP SERIES: Los Angeles defeats St. Louis, Houston beats New York
WORLD SERIES: A 2017 replay.