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Thursday, December 18, 2008
PER Diem: Dec. 18, 2008

By John Hollinger
ESPN.com

Kevin Garnett
Sorry, Kevin Garnett: There are two good reasons why your team isn't No. 1 in the Power Rankings.

"How can the Celtics be only No. 2 in the Power Rankings? After all, Cleveland has lost twice as many games as Boston, and the Celtics won when the two played head-to-head on opening night, and Cleveland has played a slightly weaker schedule."

E-mails with this question started out as a trickle to my in-box and have steadily picked up in pace with each successive Boston win.

Daily Gems
Here are John Hollinger's top five NBA observations for Wednesday. Insider Insider

• What's going on with Mike Miller?
• Awfulness of the Clippers' bench
• Rasual Butler's rise from last season
• Felton trade to Warriors?
• Utah's rally against New Jersey

What it comes down to, basically, is scoring margin and how we weight infrequent events. Let's get to scoring margin first, because it's the more cut-and-dried concept of the two: Cleveland beats its opponents by more points than Boston does. So far this season, the Cavs have outscored their opponents by 13.1 points per game, which would set a new NBA record if they keep it up.

That wouldn't be the only record they'd set. There's a predictable relationship between scoring margin and win-loss record, such that a team with an average margin of plus-13.1 points can expect to win around 74 games in an 82-game season. Those 74 wins would set the record for most wins in a season, knocking the Bulls' 72 wins in 1995-96 from the top spot.

It's unlikely that Cleveland will continue to play quite this well, of course, thanks to a phenomenon we call regression to the mean. But it's important for Celtics fans to understand how well the Cavs are playing. The Celtics' ranking of 110.9 is actually higher than it was last season when they won the championship; I'm sure Celtics fans wonder how their team can be ranked only second when it's the defending champ and is playing even better than it did last year.

But the rankings aren't done in a vacuum, and Boston isn't the only team threatening to set a historic mark this season. Even as the Celtics were outlasting Atlanta on Wednesday 88-85, the Cavs were spanking Minnesota by 23 points on the road -- the 18th time they've won by double figures in 25 games.

That takes us to our second point, how we weight infrequent events. If we judge the Power Rankings just on losses, we don't have much to go by at the top -- the two Eastern heavyweights have lost a combined five times when they weren't playing each other. In fact, the disparity between the two in the standings effectively hinges on the opening night result, which in turn hinges on just a couple of shots in a game played nearly two months ago.

Boston's superiority in win-loss record is mainly a result of its fortune in close games. The Celtics are 7-0 in games decided by five points or fewer, including two overtime wins. The Cavs, meanwhile, are 1-2 in those contests. Because these games are essentially 50-50 propositions, Boston's mark likely isn't sustainable. Put another way, it's clearly unreasonable to expect that the Celtics will finish the year 22-0 in games decided by five points or fewer.

Knowing that information makes it much easier to see why the Power Rankings keep Cleveland ahead of Boston. If the Celtics were a more normal 4-3 in the close ones, their overall mark would be 21-5, which would put them a half-game behind the Cavs. As awesome as Boston has been, the Cavs have been more dominant in the early going. If the trend continues, the win-loss records eventually will reflect what the point margins already tell us.

John Hollinger writes for ESPN Insider. To e-mail him, click here.