The Modified PPP (Points-Per-Possession) Stat

In the midst of a stimulating discussion with keven at LMF, I had a rare moment of clarity regarding the widely-used "points-per-possession" stat and a way that I believe it could be improved to more accurately reflect a player's scoring efficiency.

The formula keven uses is PTS/(FGA+(FTA*.5)+TO). That's the traditional formula I've seen. The formula developed by John Hollinger is PTS/(FGA+(FTA*.44)+TO-OREB). The Hollinger formula accounts for offensive rebounds and situations where the player scores and gets fouled, receiving one foul shot. I think both formulas have problems.

Since we're trying to use the PPP to track scoring efficiency, it's not fair to give full weight to an offensive rebound, because a lot of times a player gets an offensive rebound and then passes the ball. An appropriate formula would give the player credit if they grabbed an offensive rebound and then scored. I'm not sure, however, that such a stat is tracked. 82games.com tracks the percentage of FGAs that are "tips", but that wouldn't account for all putbacks.

The other major flaw in both formulas is that they give too much weight to turnovers. If you're trying to track scoring efficiency, the only turnovers you would count would be turnovers committed while trying to score. For example:

• offensive fouls when the player is handling the ball
• offensive fouls when the player is trying to establish post position
• offensive fouls when the player pushes off to get free of a defender
• losing the ball off the dribble or being stripped of the ball
• three second calls when the player has the ball; and
• traveling/palming/double-dribbling violations.

You wouldn't count turnovers that are committed when the player isn't trying to score. For example:

• a bad pass
• an offensive foul off the ball
• a moving screen/pick
• three second calls when the player doesn't have the ball; and
• five-second calls inbounding the ball

Giving weight to all ballhandling turnovers is probably unfair, because it adversely affects the rating of players with greater ballhandling responsibility in the offense, but no stat is perfect. 82games.com tracks turnovers and categorizes them into offensive fouls, bad passes, ballhandling turnovers, and other turnovers. That's also not perfect, however, since it doesn't differentiate between offensive fouls committed off the ball and offensive fouls committed while trying to score.

So what's the solution? I suppose that a reasonable compromise would be for us to use the data that we have available to tweak the formula such that it's at least as accurate as it can be. I'd propose the following formula:

POINTS/(FGA+(FTA*.44)+(Offensive Fouls+Ball Handling Turnovers)-Tips

This improved formula doesn't give weight to "non-scoring" turnovers like bad passes. That way we can use data from the statistics the NBA keeps and statistics that 82games keeps to at least give a more appropriate weight to turnovers and offensive rebounds.

Applying the above formula (using the stats as they stood before last night's game):

Stackhouse
points-----------616
FGA-------------483
FTA-------------224
Offensive fouls---15
Ballhandling TOs--27
Tips-------------5
Modified PPP ----.996

Finley
points----------497
FGA------------446
FTA------------78
Offensive fouls--4
Ballhandling TOs-11
Tips-------------0
Modified PPP-----1.00

Nowitzki
points----------1145
FGA------------832
FTA------------400
Offensive fouls--15
Ballhandling TOs-27
Tips-------------8
Modified PPP-----1.10

Terry
points----------490
FGA------------355
FTA------------72
Offensive fouls--7
Ballhandling TOs-21
Tips------------0
Modified PPP----1.18

Dampier
points----------377
FGA------------268
FTA------------149
Offensive fouls--13
Ballhandling TOs-31
Tips------------29
Modified PPP----1.08

Howard
points----------445
FGA------------381
FTA------------106
Offensive fouls--10
Ballhandling TOs-18
Tips------------15
Modified PPP----1.01

I think that this "modified PPP" more accurately reflects players' relative scoring efficiency.

Oh well, that's my two cents for today. Hopefully I'll have more blog entries coming soon regarding the Mavs' season so far and what the rest of the year holds for them...