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Tuesday, May 8, 2012
Championship experience matters

By Henry Abbott

On his blog at Skeptical Sports, current TrueHoop Stat Geek Smackdown champion Benjamin Morris talks about a surprisingly simple method of picking NBA champions. It has a heck of a lot to do with the fact that teams that have won titles are more likely to win more, for whatever reason:
Perhaps this will change going forward, but, historically, there are no two ways to cut it: No matter how awesomely designed and complicated your models/simulations are, if you don’t account for championship experience, you will lose to even the most rudimentary model that does.

So case in point, I came up with this 2-step method for picking NBA Champions:
Following this method, you would correctly pick the eventual NBA Champion in 64.3% of years since the league moved to a 16-team playoff in 1984 (with due respect to the slayer, I call this my “5-by-53 model ).

Of course, thinking back, it seems like picking the winner is sometimes easy, as the league often has an obvious “best team” that is extremely unlikely to ever lose a 7 game series. So perhaps the better question to ask is: How much do you gain by including the championship test in step 1?

The answer is: a lot. Over the same period, the team with the league’s best record has won only 10/28 championships, or ~35%. So the 5-by-5 model almost doubles your hit rate.

And in case you’re wondering, using Margin of Victory, SRS, or any other advanced stat instead of W-L record doesn’t help: other methods vary from doing slightly worse to slightly better.

The last five champions are the Mavericks, Lakers, Lakers, Celtics and Spurs. Of them, only San Antonio was within five games of the best record.

Therefore, this model, which has predicted so much better than fancier seeming metrics, predicts the Spurs will take it all this year. Very interesting.

The question is, why? Why are teams that have won before so much better at winning again? I'll kick off the brainstorming:
Anyway, it's certainly fascinating.

UPDATE: John Hollinger with a good point that fits this and other data: Maybe title-winning team don't value the regular season much.