Very early on Monday morning Henry Abbott – of TrueHoop – posted the following:
June 15, 2009 1:29 AM
Berri, the lead author of the Wages of Wins, beat ESPN’s John Hollinger by seven points. Hollinger picked every series of the playoffs right, except for three — Houston vs. Portland in the first round, and both Conference Finals. Berri, meanwhile, correctly predicted that the Lakers would beat the Nuggets.
Soon afterwards my phone just started ringing. Members of the media from around the world kept calling, wondering the secret to my victory. And here is the story I told…
It all began when the Lakers acquired Pau Gasol. At the time Andrew Bynum was still hurt. But I argued that once Bynum was healthy, the Lakers with Kobe Bryant, Gasol, Bynum (as well as Trevor Ariza and Lamar Odom), would be the favorites to win the NBA title. That was my argument in the midst of the 2008 NBA Finals (when Bynum was still hurt). And that was what I argued at the onset of the 2008-09 season.
Now that the Lakers have indeed won the 2009 NBA Championship we can take a step back and evaluate my immense predictive powers. Not only did I correctly identify the winner in thirteen of the fifteen 2009 playoff series, I also correctly identified the NBA champion in 2009 more than twelve months before it happened. Such a result clearly indicates that what is said about basketball in The Wages of Wins is correct.
Let’s take a step back and identify two problems with the previous two paragraphs.
1. Okay, no one actually called me (not even Henry).
2. Although I did pick the Lakers to win more than 12 months ago, one crucial detail was incorrect. The key to the Lakers was going to be the return of Andrew Bynum. Bynum the person did return to the court, but the Bynum we saw in 2007-08 did not. In 2007-08, Bynum posted a WP48 [Wins Produced per 48 minutes] of 0.394 (average is 0.100). This past season his WP48 was 0.198. Such a mark is quite good, but not nearly as good as what we saw in 2007-08. Plus, Bynum was again hurt. In 2007-08 he only played 35 games before a season ending injury. This past season he only managed to appear in 50 games.
When we look at Bynum we see a clear decline in performance. This could be due to
- Bynum’s injury problems.
- diminishing returns (the team did add Gasol), although this effect tends not to be so large.
- the possibility that what Bynum did in 1,008 minutes in 2007-08 was not representative of what he will do over time in the NBA.
All three explanations might have some validity (although, once again, the diminishing returns story probably cannot explain the size of the decline we observe). Regardless, I assumed Bynum would return to what we saw in 2007-08 and therefore concluded the Lakers were the clear favorite to win the title in 2009. The Lakers did win, but I am not sure that would have happened if Orlando didn’t upset Cleveland. In fact, I was quite happy to see that upset. Picking LA to beat Orlando seemed much easier than trying to guess if Cleveland or LA would be victorious in the NBA’s Kobe-LeBron dream finals.
Learning from the Smackdown
So what have we learned from the entire TrueHoop Smackdown experience?
Picking playoff games is really not a very good test of a model or someone’s analytical skills. As I have been saying all along (see HERE and HERE and HERE), a seven game series is too short for predictions to be made with perfect accuracy. In other words, the best model can be done in by the randomness of a small sample.
That being said, I think we have some evidence for the elements of a “best” model (at least “best” under the circumstances of the playoffs). Two years ago I lost to Justin Kubatko in this contest. As I noted at the time, both of us made our picks according to a team’s efficiency differential. Kubatko, though, considered home court advantage and I did not. Because both efficiency differential and home court advantage matter (and this can be seen statistically), Kubatko had the better model and he probably deserved to win.
Last year I did not participate and Kubatko repeated as champion. This year I was back and Kubatko was absent. But with a model based on efficiency differential and home court advantage I was victorious. So we have now seen three consecutive seasons where the person who only considered these two factors managed to win the contest. Once again, the playoffs are not strictly pre-determined by these two factors. Upsets can and will happen. And when this happens – as I have argued – one must try and resist the urge to cling to ad hoc explanations. In other words, sometimes s**t happens, and when that happens that should be your explanation.
Of course, you can’t say s**t on TV. This must be why people on TV feel the need to offer ad hoc explanations (then again, maybe not).
The WoW Journal Comments Policy
Our research on the NBA was summarized HERE.
Wins Produced, Win Score, and PAWSmin are also discussed in the following posts:
Finally, A Guide to Evaluating Models contains useful hints on how to interpret and evaluate statistical models.