The post season: It’s mostly luck

ESPN asked 70 “experts” who will win the World Series, and 37 picked the Nationals. So, the Nats are sure to win, right? Sorry.

I’ve understood for a long-time that MLB post-season series are mostly luck—the best team usually doesn’t win it all. When reading an article from Neil Payne at fivethirtyeight.com, I thought of a way to explain this idea.

According to Payne, in a typical 7-game baseball post-season series, the better team will actually win about two-thirds (66%) of the time. So I thought of this analogy.

Let’s suppose that there are two types of coins in a bucket—one type of coin “A” has the logo of the better team on both sides of the coin. If you select that coin and flip it, you are guaranteed that the better team wins. The other type of coin “B” is an ordinary random coin with the logos of each team on the two sides. If you select that coin and flip it, there’s a 50-50 chance that the better team wins. You’re going to randomly pick one coin from the bucket and flip it. In order for the better team to win two-thirds of the time, what proportion of the coins in the bucket need to be random (that is, coin “B”)?

If you remember a little bit of high school probability and play around with it, I think you’ll see that you’ll get the correct outcome if two thirds of the coins in the bucket are random (“B”), and one third are pre-set for the better team to win (“A”). (For example, if I select six coins, on average two of them will be coin “A” which will both show the better team, and four of them will “B,” for which on average two will show the better team, giving me the better team winning on average in 4 of 6 cases, or two-thirds of the time.) I think I’d describe that situation by saying the outcome is two-thirds random, and one-third the better team wining.

Payne also mentions that in a single-game playoff, such as the wildcard game, the better team wins about 57% of the time. If I’ve done the math correctly, that works out to be roughly six-sevenths random chance and one-seventh the better team winning.

If we put everything together and ask what are the chances that the best of the 8 teams making the divisional series goes on to win the World Series, the math is trickier. But similar calculations indicate that it’s roughly nine-tenths random chance and one-tenth the best team winning.

So, I’ll go ahead and issue the proverbial wish—may the best team win. But don’t be surprised if it doesn’t.