This is how…

My buddy Idris scraped some historical NBA data from the web and calculated the weighted average age of each team in every year. Then we noted the champions in each year and plotted the data to see if there were any interesting patterns.

… And there were:
Young teams hardly ever win championships.
Championship teams are significantly older than average, and they get older as they continue to win.

This chart inspired an infographic: Teams That Stay Together, Win Together

Let me explain this data. Basically, team age can be used as a proxy for team cohesion.

When I analyzed championship teams during the eras that they were winning — The Celtics and Lakers in the 80′s, the Bulls in the 90′s, and the Lakers and Spurs in the 00′s — I found that these teams had a core group of guys that had been playing together for 8, 9, 10, and sometimes even 11 and 12 years. Having older players is an unavoidable consequence of having this amount of shared history on the court. Teams that win have higher player retention because they want to keep a good thing going.

I looked at non-winning teams and found that they generally had players that had been together for 3, 4, or 5 years at most. Teams that don’t win have general managers that trade and buy players, attempting to assemble a viable team. Players move on from non-winning teams in hopes of getting a better shot at ring.

When you look at this year’s Playoff contenders by age in the chart to the right, you see that Dallas is at the top of the list at 31.2 years old, which is the basis of my prediction. Los Angeles and Boston are also old teams and have long Finals legacies but that doesn’t matter here.

The Dallas Mavericks will win the 2011 Finals.

It’s a simplistic theory, and that’s what I’m hanging my hat on. It’s not talent or experience alone that wins championships, it’s talented players that stick together. Their shared experiences allow them to cooperate better on the court, which makes them more potent competitors over time and thus more likely to win championships. So, in this model, the oldest team wins.

Data scraped from basketball-reference.com