Friday, June 11, 2010
Is Bill James’ temperature a leading indicator?
Posted by Dave StudemanWarning: nerd post. I'm actually playing with baseball stats instead of watching a game because my son is playing Call of Duty on the TV.
At Bill James Online (subscription site), Bill keeps track of each team's "temperature." The idea is to literally measure how "hot" or "cold" each team is. The system is calculated so that an average team has a room temperature of 72 degrees. The specific math is simple:
1. Each team's temperature at the start of the season is 72 degrees
2. After each game, multiply the team's pre-game temperature by .8958334
3. If they won the game, add 15 degrees
This system reminds me of Win Shares. I have no idea how he came up with the math (seven digits for the multiplier? Really?), but it seems to "work" in its own way. Essentially, the multiplier acts to "regress" the team's record because 90% of a 120 degree temperature is a lot more than 90% of a 40 degree temperature.
Let's look at the temperature in action. Here is a graph of the Braves' record this season (the blue line showing games above/below .500) and their temperature (the red dotted line):
I purposely set the scale so that a .500 record is roughly on the same level as 72 degrees. On June 3, the Braves reached a higher temperature (122 degrees) than any other team this year.
The cool thing is that the Braves' temperature has seemingly been a leading indicator of their record. When the red line has been above the blue, the blue line has risen. When it's fallen below, their record has fallen.
Having said that, I don't actually believe the Bill James Temp consistently acts as a leading indicator. But it does make a cool graph.
Dave was called a "national treasure" by Rob Neyer. Seriously. Comments about this article can be sent to him through the miracle of e-mail.
It’s a little hard to tell, but it looks like you plotted the temperature after the game, when you should look at it before the game. (Temperature is peaking at the same time as their winning percentage; it should peak the day after, since it doesn’t come down until they actually lose.)