APBRmetrics

Posted: **Fri Nov 18, 2016 4:25 pm**

Does anyone know why ortg/drtg values are different on nba.com than on basketball-reference or nbawowy? Which source would have more accurate data on team and individual level?

Posted: **Sun Nov 20, 2016 7:00 pm**

There are multiple different ways to estimate possessions, as outlined here:
http://nyloncalculus.com/2015/12/21/nyl ... ssessions/

From a technical perspective, the Basketball-Reference formula offers the closest estimates to our working definition of possessions. However, they're close enough that I wouldn't really say one is better or worse. The issue is largely in comparing ratings across sites (e.g. saying where a team's offensive rating from NBAwowy would rank on NBA.com/Stats).

Posted: **Sun Nov 20, 2016 11:21 pm**

I will use 2 games as examples.

2013 finals game 1

http://stats.nba.com/game/#!/0041200401/advanced/
MIA 102.9 ortg
SAS 102..3 ortg
87.7 pace
(negative net for Spurs despite winning the game)

http://www.basketball-reference.com/box ... 60MIA.html
MIA 103.5 ortg
SAS 108.2 ortg
85.0 pace

If we will count possessions manually from play by play, then Miami had 86 poss, Spurs 84, so game pace 85 and ortgs exctly as b-r says.

UTA-HOU 16.11.19

http://stats.nba.com/game/#!/0021600184/
UTA 110.3 ortg
HOU 113.5 ortg
95.1 pace

http://www.basketball-reference.com/box ... 90HOU.html
UTA 111.2 ortg
HOU 121.1 ortg
91.7 pace

http://nbawowy-52108.onmodulus.net/purr ... 242adu0udi
(if I understand correctly nbawowy doesn’t use formulas for possessions, but takes data directly from play by play)
UTA 109.7 ortg
HOU 119.4 ortg
93.0 pace

So doesn't it look like something is wrong with stats.nba.com?

Posted: **Mon Nov 21, 2016 5:49 am**

As explained in the above link, using the stats.nba.com formula overestimates the number of possessions because it doesn't account for team offensive rebounds. In an individual game, that (as well as the estimate for free throw possessions that any estimator uses) mean the net ratings can get a little wonky. Over larger samples, they're likely to even out.

Posted: **Mon Nov 21, 2016 7:39 am**

Kevin Pelton wrote:As explained in the above link, using the stats.nba.com formula overestimates the number of possessions because it doesn't account for team offensive rebounds. In an individual game, that (as well as the estimate for free throw possessions that any estimator uses) mean the net ratings can get a little wonky. Over larger samples, they're likely to even out.

So lets look at larger samples. 2015/16 season:

76ers
wowy 100.0 ortg, 111.2 drtg, 96.8 pace
b-r 98.8 ortg, 109.2 drtg, 97.9 pace
nba.com 96.6 ortg, 106.7 drtg, 100.2 pace

Bucks
wowy 105.0 ortg, 109.3 drtg, 93.2 pace
b-r 104.3 ortg, 108.7 drtg, 94.2 pace
nba.com 102.2 ortg, 105.7 drtg, 96.6 pace

and so on. So it looks like nba.com's values are constantly less accurate than from b-r (assuming wowy uses pbp, so has real values).

Posted: **Mon Nov 21, 2016 10:50 am**

2015/16 regular season:

Code: Select all

b-r ORTG	nba ORTG		wowy ORTG	b-r vs wowy		nba vs wowy		TEAM
105,1		103,0			105,9		-0,8					-2,9		Atlanta Hawks
106,8		103,9			107,2		-0,4					-3,3		Boston Celtics
103,2		100,9			103,9		-0,7					-3		Brooklyn Nets
107,1		105,1			107,9		-0,8					-2,8		Charlotte Hornets
105,0		102,1			105,6		-0,6					-3,5		Chicago Bulls
110,9		108,1			111,4		-0,5					-3,3		Cleveland Cavaliers
106,7		104,8			106,7		0,0					-1,9		Dallas Mavericks
105,6		102,7			107,1		-1,5					-4,4		Denver Nuggets
106,1		103,3			106,7		-0,6					-3,4		Detroit Pistons
114,5		112,5			114,9		-0,4					-2,4		Golden State Warriors
108,3		105,5			108,8		-0,5					-3,3		Houston Rockets
104,6		102,4			104,9		-0,3					-2,5		Indiana Pacers
108,3		106,5			108,8		-0,5					-2,3		LA Clippers
101,6		98,6			101,9		-0,3					-3,3		Los Angeles Lakers
105,4		102,6			105,7		-0,3					-3,1		Memphis Grizzlies
106,1		104,2			107,2		-1,1					-3		Miami Heat
104,3		102,2			104,9		-0,6					-2,7		Milwaukee Bucks
106,5		104,3			106,5		0,0					-2,2		Minnesota Timberwolves
105,6		103,2			106,3		-0,7					-3,1		New Orleans Pelicans
104,6		102,0			105,2		-0,6					-3,2		New York Knicks
113,1		109,9			113,6		-0,5					-3,7		Oklahoma City Thunder
105,1		102,6			105,8		-0,7					-3,2		Orlando Magic
98,8		96,6			100,0		-1,2					-3,4		Philadelphia 76ers
102,2		99,4			102,4		-0,2					-3		Phoenix Suns
108,8		106,1			108,9		-0,1					-2,8		Portland Trail Blazers
106,0		103,3			106,5		-0,5					-3,2		Sacramento Kings
110,3		108,4			110,5		-0,2					-2,1		San Antonio Spurs
110,0		107,0			110,9		-0,9					-3,9		Toronto Raptors
105,9		103,1			106,7		-0,8					-3,6		Utah Jazz
105,3		102,9			105,7		-0,4					-2,8		Washington Wizards
106,4		103,9			107,0		-0,6					-3,0		AVG

Code: Select all

b-r DRTG	nba DRTG		wowy DRTG	b-r vs wowy		nba vs wowy		TEAM
101,4		98,8			103,0		-1,6					-4,2		Atlanta Hawks
103,6		100,9			104,0		-0,4					-3,1		Boston Celtics
110,9		108,5			111,5		-0,6					-3,0		Brooklyn Nets
104,3		101,8			105,1		-0,8					-3,3		Charlotte Hornets
106,5		103,9			107,0		-0,5					-3,1		Chicago Bulls
104,5		102,3			105,1		-0,6					-2,8		Cleveland Cavaliers
107,0		104,3			107,2		-0,2					-2,9		Dallas Mavericks
108,9		106,4			111,3		-2,4					-4,9		Denver Nuggets
105,5		103,4			106,0		-0,5					-2,6		Detroit Pistons
103,8		100,9			104,1		-0,3					-3,2		Golden State Warriors
108,1		105,6			108,6		-0,5					-3,0		Houston Rockets
102,9		100,2			103,3		-0,4					-3,1		Indiana Pacers
103,8		100,9			104,4		-0,6					-3,5		LA Clippers
111,6		109,3			111,8		-0,2					-2,5		Los Angeles Lakers
107,8		105,4			108,3		-0,5					-2,9		Memphis Grizzlies
104,4		101,5			105,3		-0,9					-3,8		Miami Heat
108,7		105,7			109,2		-0,5					-3,5		Milwaukee Bucks
110,1		107,1			110,7		-0,6					-3,6		Minnesota Timberwolves
109,5		107,3			110,0		-0,5					-2,7		New Orleans Pelicans
107,6		104,8			108,0		-0,4					-3,2		New York Knicks
105,6		103,0			106,0		-0,4					-3,0		Oklahoma City Thunder
106,8		104,6			107,3		-0,5					-2,7		Orlando Magic
109,2		106,7			111,2		-2,0					-4,5		Philadelphia 76ers
109,0		107,0			109,6		-0,6					-2,6		Phoenix Suns
108,0		105,6			108,2		-0,2					-2,6		Portland Trail Blazers
108,4		106,3			109,0		-0,6					-2,7		Sacramento Kings
99,0		96,6			99,4		-0,4					-2,8		San Antonio Spurs
105,2		102,7			106,0		-0,8					-3,3		Toronto Raptors
103,9		101,6			104,8		-0,9					-3,2		Utah Jazz
105,8		103,6			106,3		-0,5					-2,7		Washington Wizards
106,4		103,9			107,1		-0,7					-3,2		AVG

0.7/0.6 vs 3.0/3.2 looks like significant difference, doesn't it?

APBRmetrics

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