Saturday, November 10, 2007

What is PVOA

PVOA, or "point value over average" is a concept based upon the thinking behind's DVOA, or "defense adjusted value over average". What it tries to capture is how a team performed based upon how the average NBA team would have performed given the same opponent and the same number of possessions.

Here's how its calculated. You take the opponent's established offensive and defensive efficiency numbers for the season (which are pts * poss/100 and pts allowed * poss/100, respectively), then you calculate the number of possessions in the game for each team (FGA + .44FTA + TOs - Offensive rebounds), and you multiply. Then you compare it against the actual number of points scored and points allowed for the team you are evaluating.

Example: Detroit plays the LA Clippers. Detroit won the game, 103 to 79. But I want to evaluate how Detroit performed against the average. So I look up LA's offensive and defensive efficiency numbers at this point in the season. They are 108.52 and 97.72. Then I calculate the number of possessions. That turns out to be 93.92 for Detroit and 91.32 for LA.

So, to evaluate Detroit's offensive performance I multiply their number of possessions 93.29 by the number of points LA has been giving up per possession, .9772. I come up with 91.78 -- that's what the average team has been scoring against LA in that number of possessions. But Detroit scored 103, so their "point value over average" is +11.22. Then you do the same for Detroit's defense, and it turns out they gave up 20.12 points less than the Clippers average number of points in that many possessions, so Detroit's defensive PVOA is -20.12, for an outstanding overall PVOA for Detroit of +31.34 (the defensive numbers, if negative, are considered positive when calculating Detroit's overall PVOA, and vice versa for offense).

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