THE BOOK--Playing The Percentages In Baseball

Monday, August 18, 2008

Maps and Territories

Well-written article:

We all know that the map of Alberta and the territory of Alberta are two different things. The map might show that a road is straight, but when you head out to that road, you actually find that it curves here and there, that the territory itself is different than the map.  So the map is not the territory, and it never is, and it never can be. When it comes to hockey, the map is the statistics we use to try to describe the performance of a player. The territory is the player’s performance itself. The map and the territory are two different things here as well. For instance, the statistical map might say that Shawn Horcoff was +3 on the night, but really he had a terrible game. Horcoff had little to do with any of the three goals scored when he was on the ice, and on one goal against his team, after making a terrible play, he left the ice before the goal was scored, so the minus mark went to some other player, not him. When you hear then, that Horcoff played great because he was +3 and he faced strong opponents, and that’s all you know about the matter, it’s important to realize that number has great limitations in describing the performance.

There are easy ways to handle plus/minus in hockey, and that’s the With Or Without You (WOWY) method.  82games.com does that for basketball.  While the above author is correct that plus/minus has its flaws (giving a plus to someone who doesn’t deserve it, etc), that doesn’t matter.  You can take say Albert Pujols and Benjie Molina, and then, randomly give each player 200 PA of a mean of .340 OBP (that is, let a random number generator, with mean = .340, and 1 SD = .030, create a number, then multiply that by 200), and add that to his totals.  Guess what?  Pujols will still have a higher OBP than Molina.  Once in a blue moon Molina might end up with a higher OBP than Pujols because he lucked into a .600 OBP in 200 PA while Pujols lucked into a .100 OBP in 200 PA.  But, the underlying basis of OBP (and plus/minus) still holds.  The signal is still there, but now you have more noise to sift through.

Anyway, enjoyable read.