possessions formulas

[lorak]

Which one is better (more accurate):
nba.com: ((FGA - O-Rebs) + TO + (.436 x FTA))
or
basketball-reference:
0.5 * ((Tm FGA + 0.4 * Tm FTA - 1.07 * (Tm ORB / (Tm ORB + Opp DRB)) * (Tm FGA - Tm FG) + Tm TOV) + (Opp FGA + 0.4 * Opp FTA - 1.07 * (Opp ORB / (Opp ORB + Tm DRB)) * (Opp FGA - Opp FG) + Opp TOV))

?

[Chicago76]

When you compare actual tracked possessions courtesy of basketballvalue, the latter form is much closer.

The NBA's version is pretty similar to the initial Basketball on Paper simplified form that Dean Oliver put out years ago (along with the more complex formula he also published in the same book):

FGA-ORB+0.4xFTA+TOV

This form is actually a bit more accurate than the NBA's simplified version too.

FWIW: last year the NBA's possession formula would have overestimated possessions pretty consistently at a rate of roughly 2 per game. The more complex formula on average is +/- 0.3 possessions per game away from the true number.

[lorak]

Thx Chicago76. That's the answer I was looking for.