Baseball Hacks

Odds of the Best Team Winning the World Series

What are the odds of the best team winning the World Series or any seven-game series?

Let’s look at the probability of the best team winning the World Series. Obviously, this was much more likely before division play in 1969. The best team has a much better chance of getting to the Series based on a full season than on a playoff series. We can’t figure out exactly what the odds are of the best team winning. But if we take a sample for the years 1961–1968, using our simulation and assuming that the true winning percentage of each team was downgraded 20% toward the mean and that the best team was the team with the highest percentage, we get these results (where the probability of winning is based on 1,000 simulated seasons):

	year   AL  winner wins prob of     NL  winner wins prob of
	                    winning                    winning
	1961   NY  109    .730             CIN 93    .497
	1962   NY  96     .551             SF  103   .373
	1963   NY  104    .766             LA  99    .565
	1964   NY  99     .385             STL 93    .254
	1965   MIN 102    .616             LA  97    .414
	1966   BAL 97     .644             LA  95    .382
	1967   BOS 92     .306             STL 101   .709
	1968   DET 103    .781             STL 97    .649

This says that, on average, the best team in the league wins the pennant a little more than half the time, which seems reasonable. The best team overall increases that probability to around 60%.

We already stated that the probability of winning a given game is equal to . 500, plus the difference in winning percentages of the two teams. Extending the series to three, five, seven, or nine games increases the odds of the best ...