APBRmetrics Forum Index APBRmetrics
The statistical revolution will not be televised.
 
 FAQFAQ   SearchSearch   MemberlistMemberlist   UsergroupsUsergroups   RegisterRegister 
 ProfileProfile   Log in to check your private messagesLog in to check your private messages   Log inLog in 

Offensive and Defensive PER

 
Post new topic   Reply to topic    APBRmetrics Forum Index -> General discussion
View previous topic :: View next topic  
Author Message
Eli W



Joined: 01 Feb 2005
Posts: 286

PostPosted: Wed Sep 19, 2007 11:09 am    Post subject: Offensive and Defensive PER Reply with quote

At various times people have asked for a breakdown of PER into its offensive and defensive components. I'm not the biggest fan of PER, but I definitely see how it could be more useful if it wasn't just an all-in-one "lots of things that capture offensive contributions pretty well plus a few things that capture a small part of defensive contributions" statistic. Since I already had a spreadsheet that calculated PER, it wasn't that hard to create one that split it into OPER and DPER. I've posted it on the Yahoo group and it covers the last five seasons (it's called "offensive and defensive PER.xls):

http://sports.groups.yahoo.com/group/APBRmetricsFiles/files/

OPER is the offensive components of PER - 3PM, Ast, FGM, FTM, TO, missed FGA, missed FTA, and ORB. DPER is the DRB, Stl, Blk, and PF parts. The breakdown isn't perfect since it treats all fouls as defensive fouls.

A difficulty arose in deciding how to standardize OPER and DPER. I wanted to be able to fairly compare ratings from different seasons (which would mean separately standardizing both OPER and DPER), but at the same time I thought it would be interesting to see how much of a player's single-season PER came from his offensive stats and how much from his defensive stats (which would mean just standardizing total PER and then splitting it up). I think both ways of looking at it are useful, so I included both in the spreadsheet. The second method yielded OPER and DPER, which always add up to a player's PER (I just took the ratio of non-standardized OPER to non-standardized DPER and used it to break up PER). In the seasons I looked at the average breakdown of OPER to DPER was around 12 to 3 (totalling the average PER of 15). However, because the league average ratio of OPER to DPER changes every year, comparing OPER's or DPER's from different seasons can be misleading when there's no standardizing (it wasn't a big deal in the five seasons I looked at, but if one were to go back a few decades there might be significant effects). So I also listed OPER15 and DPER15, which are standardized around 15 just like PER (i.e. each season the average OPER15 and DPER15 are set at 15). I could have used a different number (and there's no reason both OPER and DPER had to be standardized around the same number), but 15 seemed to make some sense given people have some familiarity with it representing the average in PER. You'll notice that the greater variance in DPER's leads to DPER15's that are much greater than anyone's PER or OPER15.

Enough description - if that didn't make sense maybe some examples will clear things up. Here are the best OPER15 and DPER15 seasons from the last five years.

Code:
Year  Player  OPER15   OPER/DPER
----- ------- ------  ----------
02-03 McGrady  32.47  26.38/3.89
02-03 O'Neal   30.87  25.07/4.42
05-06 Bryant   30.01  24.80/3.20
06-07 Wade     29.13  24.15/4.80
05-06 James    29.04  24.01/4.06

Year  Player  DPER15   OPER/DPER
----- ------  ------  ----------
05-06 Camby    51.24  11.05/8.88
06-07 Camby    47.61  10.93/8.14
02-03 Wallace  47.02   8.38/8.83
05-06 Wallace  45.64   9.59/7.91
03-04 Wallace  44.06   8.86/8.43


Here are the average OPER's and DPER's by season (they always sum to 15) - you can see that the ratio hasn't changed that much, so standardizing isn't vital when comparing players from nearby seasons:

Code:
Year  lgOPER lgDPER
----- ------ ------
02-03  12.18   2.82
03-04  12.13   2.87
04-05  12.32   2.68
05-06  12.40   2.60
06-07  12.44   2.56


After I did all this I remembered that Hollinger had done something like this before. Looking back, I was able to find his description of Offensive PER on page 12 of his first book (Prospectus 2002), as well as in his comments on Steve Nash in Forecast 05-06 (page 229), and in one Insider article ( http://insider.espn.go.com/nba/playoffs2005/columns/story?columnist=hollinger_john&id=2041492 ). In describing it in his first book, he says, "simply break down the PER by eliminating the defensive categories (blocks, steals, personal fouls, and defensive rebounds) and it leaves the league leaders in offensive PER." However, the numbers he lists for offensive PER in all three sources differ from mine because he also leaves out offensive rebounds. I'm not sure whether that was intentional or a mistake, but for my version offensive rebounds count toward OPER and defensive rebounds count toward DPER. It also looks like he chose not to standardize separately and thus arrived at an offensive PER that when summed with defensive PER will equal PER (though he'd have to include offensive rebounds in his defensive PER, or have three breakdowns into offensive PER, rebounding PER, and defensive PER). That means the figures he listed don't allow for unbiased between-season comparisons like my OPER15 and DPER15 do.

This is all a work in progress so I'm open to any comments and suggestions, especially when it comes to dealing with the standardizing issues. Another way of presenting it that I considered was instead of having an OPER and DPER that sum to PER, just have a representation of a player's ratio of offensive to defensive parts of PER. So Camby's 05-06 season could be represented as a DPER15 of 51.24 with a 55%/45% O/D split (compared to the league average of 83%/17%), meaning 45% of his PER total came from his defensive contributions. The ratio could also be represented as 1.2-to-1 offense-to-defense, compared to the league average of 4.8-to-1. I also thought about a different way of representing standardized OPER's and DPER's. Instead of centering both around 15, I could have OPER12 and DPER3, which would allow for between-season comparisons while also retaining a sense of how much each contributed to a player's PER (since each is standardized around a figure near the league average OPER and DPER broken down from PER). But that would be just a rough estimate since 12 and 3 are approximations and the real numbers change every year.

For those interested in seeing how the calculations were made, I left the formulas in all the cells of row 2 of each sheet (02-03 Abdul-Wahad and 02-03 Atlanta), and all the necessary columns are still there even though many are hidden (between Y & AL, AN & AU, and AU & AX). I deleted the formulas and just left the values in all the other cells to cut down the file size, and I hid a lot of the columns so that those who just want to see the end results don't have to wade through all the clutter.
_________________
Eli W. (formerly John Quincy)
CountTheBasket.com
Back to top
View user's profile Send private message Send e-mail Visit poster's website
Mountain



Joined: 13 Mar 2007
Posts: 216

PostPosted: Wed Sep 19, 2007 11:27 am    Post subject: Reply with quote

Thanks very much. This should be interesting to check out. OPER15 and DPER15 are excellent followthough contributions that I have wanted to look at. Your database will also allow the by position sorts and potentially position adjusted OPER15s and DPER15s.

I thought the offense representation might be 3-1 over defense, but 4-1 exceeded that expectation and solidly demonstrates that roll-up PER (lacking any shot defense plug) is mostly an offensive metric.

Have any interest in calculating team PER and offensive and defensive splits and comparing the results to the efficiencies and point differential? I might try further on that later with what you've kindly provided.
Back to top
View user's profile Send private message
Mountain



Joined: 13 Mar 2007
Posts: 216

PostPosted: Wed Sep 19, 2007 12:01 pm    Post subject: Reply with quote

06-07 league,
all players as assigned to position in JQ's database

Pos Min PER OPER DPER OPER15 DPER15

C Total 93071 889.0 663.9 225.2 800.7 1317.4
PF Total116826 1357.9 1104.7 253.1 1332.5 1481.0
SF Total126662 1202.8 989.6 213.3 1193.6 1247.9
SG Total111207 1032.4 865.7 166.7 1044.1 975.5
PG Total148226 1452.1 1265.1 186.9 1526.0 1093.6
GrandTotal600704 5981.8 4927.9 1053.8 5943.8 6166.0


Averages

Center
Min 1012
PER 9.7
OPER 7.2
DPER 2.4
OPER15 8.7
DPER15 14.3

Power Forward
Min 1123
PER 13.1
OPER 10.6
DPER 2.4
OPER15 12.8
DPER15 14.2

Small Foward
Min 1254
PER 11.9
OPER 9.8
DPER 2.1
OPER15 11.8
DPER15 12.4

Shooting Guard
Min 1293
PER 12.0
OPER 10.1
DPER 1.9
OPER15 12.1
DPER15 11.3

Point Guard
Min 1323
PER 13.0
OPER 11.3
DPER 1.7
OPER15 13.6
DPER15 9.8


All
Min 1233
PER 12.3
OPER 10.1
DPER 2.2
OPER15 12.2
DPER15 12.7


Last edited by Mountain on Wed Sep 19, 2007 1:48 pm; edited 1 time in total
Back to top
View user's profile Send private message
Statman



Joined: 20 Feb 2005
Posts: 79

PostPosted: Wed Sep 19, 2007 12:38 pm    Post subject: Reply with quote

Why not seperate into 4 - shooting/scoring, ballhandling/passing, rebounding, & defense?
_________________
www.goodstats.net
Back to top
View user's profile Send private message Send e-mail Visit poster's website
Mountain



Joined: 13 Mar 2007
Posts: 216

PostPosted: Wed Sep 19, 2007 1:55 pm    Post subject: Reply with quote

That could be an additional cut. Raw player 4 factor data is another approach.

Looks like big man offensive PER a bit more than 10% less than perimeter but defensive PER is a bit more than 20% higher.

Players could be grouped in to groups that conform with positional bias on which side of PER is higher or not. Lineups could be analyzed in this way too.
Back to top
View user's profile Send private message
S.K.



Joined: 18 Feb 2005
Posts: 52
Location: Toronto

PostPosted: Thu Sep 20, 2007 9:31 am    Post subject: Reply with quote

When playing Fastbreak Basketball I used to split my PER calculations into "on the ball" (shooting, assists, TO) and "off the ball" (rebounds, steals, blocks, fouls)... I always meant to do this with real basketball and see if the numbers were meaningful but never got around to it.
_________________
No books - no articles - no website.
Just opinions.

Ill-informed opinions.
Back to top
View user's profile Send private message Send e-mail MSN Messenger
Display posts from previous:   
Post new topic   Reply to topic    APBRmetrics Forum Index -> General discussion All times are GMT - 5 Hours
Page 1 of 1

 
Jump to:  
You cannot post new topics in this forum
You cannot reply to topics in this forum
You cannot edit your posts in this forum
You cannot delete your posts in this forum
You cannot vote in polls in this forum


Powered by phpBB © 2001, 2005 phpBB Group