Tuesday, September 25, 2007

The updated "Wages of Wins"

My copy of the updated paperback edition of "The Wages of Wins" arrived today. A list of differences between the old edition and the new can be found at the authors' website here; generally, some of the tables are updated for the 2006 seasons, but the content is almost all the same.

The most significant difference is that
the authors changed the formula for QB Score. An interception used to be worth –50 yards; now it's only worth –30. Their explanation is that when they reran their regression with better data – specifically, starting field position of drives – the coefficient came out different. Actually, it came out to –35 yards, but the authors use –30 because it's easier to remember.

Another small change I happened to notice is in the discussion of NBA players' playoff performances. The first edition of the book noted that "Win Scores" drop in the playoffs because of team defense improves in the post-season.
I argued that the difference was probably due to the fact that playoff teams face only other playoff teams; the absence of games against cellar-dwellers would reduce offensive stats. The authors apparently agree – they now added a line to say that "teams in the playoffs tend to be better, with better defenses." However, a few sentences later, they let stand an assertion that teams play better defense in the post-season. That implies that the defense of an individual team improves. I don't know if they still think this is true, or if they've changed their minds about it.

While I'm here, one other thing I noticed (in both editions) that I hadn't mentioned before.

At one point, the book looks at Michael Jordan's year-by-year record in the regular season, and compare it to his playoff performance. It turns out that in 11 of the 13 seasons, his performance declined. The authors note, of course, that performance does decline in the playoffs, by an average .03 units of "Win Score per Minute." But if you adjust by the .03, Jordan still only goes from 2-11 to 5-8.

However, the decline of .03 is an overall average for all players. But Jordan's overall score is more than twice the average. If that's the case, shouldn't his decline also be twice the average -- .06 instead of .03? That is, the average player drops by 23% (.03 divided by the average .128) because of the better competition. Shouldn't Jordan drop by the same percentage, rather than by the same raw number?

If you adjust his numbers by .06, instead of .03, Jordan now goes 10-3, which now coincides with his reputation as a clutch playoff performer.

Now, I don’t know for sure if you should indeed adjust Jordan by .06, or .03, or some other number entirely. You'd probably want to examine players with high Win Scores to see what the typical decline is. In any case, without knowing the right number, it's hard to analyze anyone's clutch performance this way.

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