Birnbaum: Accurate prediction and the speed of light

From SABR member Phil Birnbaum at Sabermetric Research on April 14, 2014:

There’s a natural “speed of light” limitation on how accurate pre-season predictions can be.  For a baseball season, that lower bound is 6.4 games out of 162.  That is, even if you were to know everything that can possibly be known about a team’s talent — including future injuries — the expected SD of your prediction errors could never be less than 6.4.   (Of course, you could beat 6.4 by plain luck.)

Some commenters at FiveThirtyEight disagree with that position.  One explicitly argued that the limit is zero — which implies that, if you had enough information, you could be expected to get every team exactly right.  That opinion isn’t an outlier  — other commenters agreed, and the original comment got five “likes,” more than any other comment on the post where it appeared.


Suppose it *were* possible to get the win total exactly right. By studying the teams and players intently, you could figure out, for instance, that the 2014 Los Angeles Dodgers would definitely go 92-70.

Now, after 161 games, the Dodgers would have to be 91-70 or 92-69.  For them to finish 92-70 either way, you would have to *know*, before the last game, whether it would be a win or a loss.  If there were any doubt at all, there would be a chance the prediction wouldn’t be right.

Therefore, if you believe there is no natural limit to how accurate you can get in predicting a season, you have to believe that it is also possible to predict game 162 with 100% accuracy.

Do you really want to bite that bullet?  

Read the full article here:

Originally published: April 15, 2014. Last Updated: April 15, 2014.