Birnbaum: Why the 2016 AL was harder to predict than the NL

From SABR member Phil Birnbaum at Sabermetric Research on October 24, 2016:

In 2016, team forecasts for the National League turned out more accurate than they had any right to be, with FiveThirtyEight’s predictions coming in with a standard error (SD) of only 4.5 wins. The forecasts for the American League, however, weren’t nearly as accurate … FiveThirtyEight came in at 8.9, and Bovada at 8.8.

That isn’t all that great. You could have hit 11.1 just by predicting each team to duplicate their 2015 record. And, 11 wins is about what you’d get most years if you just forecasted every team at 81-81.

Which is kind of what the forecasters did! Well, not every team at 81-81 exactly, but every team *close* to 81-81. If you look at FiveThirtyEight’s actual predictions, you’ll see that they had a standard deviation of only 3.4 wins. No team was predicted to win or lose more than 87 games.

Generally, team talent has an SD of around 9 wins. If you were a perfect evaluator of talent, your forecasts would also have an SD of 9. If, however, you acknowledge that there are things that you don’t know (and many that can’t be known, like injuries and suspensions), you’ll forecast with an SD somewhat less than 9 — maybe 6 or 7.

But, 3.4? That seems way too narrow.

Read the full article here:

Originally published: October 24, 2016. Last Updated: October 24, 2016.