Before the season started we learned that Yao Ming wasn’t going to play. Furthermore, Ron Artest had departed for LA and the availability of Tracy McGrady was questionable. These three players led the Rockets in points per game in 2008-09. With so much scoring exiting the building, many NBA observers thought Houston was destined for the 2010 lottery.
In looking over Houston’s roster, though, it didn’t appear this team was quite as bad as people thought. Entering this season the Rockets roster included the following players who were above average performers in 2008-09: Trevor Ariza, Shane Battier, Chuck Hayes, Kyle Lowry, and Carl Landry. Although these players were not scorers, their respective WP48 [Wins Produced per 48 minutes] numbers suggested the cupboard wasn’t bare in Houston. In fact – although the loss of Ming and McGrady was going to hurt some (notice I left out Artest) – it seemed that the playoffs were still a possibility for the Rockets.
The Rockets Today
The Rockets have now played 27 games in 2009-10. And if the season ended today, the Rockets would not have a seat at the NBA lottery. So how was this possible?
Table One: The Houston Rockets after 27 Games in 2009-10
Table One reports the Wins Produced and WP48 numbers for the Rockets this season. As one can see, the following players have so far been above average (average is 0.100): Luis Scola, Carl Landry, Kyle Lowry, Trevor Ariza, and Chuck Hayes. Yes, five of the six players who were above average last season are still above average this season.
Again, the loss of Ming and McGrady (the latter only recently returned) didn’t help. But the Rockets are still on pace to win about 46 games this season (after winning 53 last season). So apparently losing your top scorers is not necessarily a death sentence.
The performance of the Rockets this season demonstrates an aspect of basketball performance often noted in this forum. Basketball players – relative to what we see in baseball and football – are very consistent over time. For the most part, the productivity of the players the Rockets are employing this season is not much different from what we saw last year. Yes, the loss of the team’s primary scorers has forced other players to take shots. In general, though, the increase in shot attempts hasn’t reduced each player’s effectiveness.
The Ariza Story
As a few commentators on the Miami Heat post from a few days ago noted, though, the exception is Trevor Ariza (how we went from a discussion of Dwyane Wade to Ariza, though, is a mystery to me). Last season Ariza took 14.1 field goal attempts per 48 minutes (FGA48) and his adjusted field goal percentage was 51.1%. This season, Ariza’s FGA48 has increased to 20.4 and his adjusted field goal percentage has fallen to 45.8%. And this has led some people to argue that Ariza is the classic example of how increasing shot attempts lowers efficiency.
In reading the comments I am somewhat convinced I cannot change everyone’s mind about the meaning behind Ariza’s numbers. In fact, one commentator explicitly stated: “If a statistical study suggests otherwise, it must be missing something.”
Such a comment forces me to lower my expectations. The following comments on Ariza’s declining field goal percentage, as I note, will not necessarily change minds (but they might give “true believers” something else to rationalize away). Here are some things to think about when you consider Ariza’s drop in efficiency:
- Ariza’s career adjusted field goal percentage is 48.4%. So his mark this year is not far from this career mark.
- Ariza, though, has dropped off. Looking at other players on Houston’s roster, though, reveals a different story. Carl Landry is taking 5.6 additional field goals per 48 minutes and his shooting efficiency has only declined from 57.5% to 57.0%. Chuck Hayes has seen his FGA48 rise by 4.9 and his shooting efficiency has improved by 7.7%.
- The discussion of Ariza, Landry, and Hayes is purely anecdotal. When you look at players from 1977-78 to 2007-08 (the sample includes over 5,000 season observations) you see that there is a link between a change in the number of shots he takes and his shooting efficiency. But the impact is quite small. Here is what we say in our next book: “…imagine a player who takes 16.3 shots per 48 minutes and has an adjusted field goal percentage of 48.4% (these are the league average marks). If that player increased his shots per 48 minutes to 25.3 (a two standard deviation increase), his adjusted field goal percentage would be expected to decline to 47.1%.”
Given all this, is the change we see in Ariza’s shooting efficiency simply due to the fact he is being asked to take more shots? I don’t think the evidence leads to that conclusion. We don’t see the same story when we look at the other players on the Rockets (who are also taking more shots). And we don’t see such a strong link between shot attempts and shooting efficiency when we look at a sample of over 5,000 NBA players.
All that being said, I don’t have a great story for why Ariza’s efficiency has declined. I will note that although NBA players are very consistent from season to season, shooting efficiency is one aspect of a player’s performance that is the most volatile (as we note in the next book, it’s about as volatile as OPS and Slugging Percentage in baseball).
The Bigger Story
Regardless of how you see the Ariza story, the primary observation remains. Most players on the Rockets are playing about as well as we would expect given their past performance. Yes, many of these players are playing more minutes. And many are taking more shots. But their overall effectiveness is roughly the same.
Now it’s important to remember that losing Ming and McGrady didn’t help. And although the Rockets would be in the playoffs if the post-season started today, they are only barely in. There’s still a chance Houston will be visiting the lottery. That being said, what we have seen so far does suggest that losing your top scorers doesn’t necessarily kill an NBA team. At least, that’s what we see when a roster has an abundance of productive non-scorers.
– DJ
The WoW Journal Comments Policy
Our research on the NBA was summarized HERE.
The Technical Notes at wagesofwins.com provides substantially more information on the published research behind Wins Produced and Win Score
Wins Produced, Win Score, and PAWSmin are also discussed in the following posts:
Simple Models of Player Performance
What Wins Produced Says and What It Does Not Say
Introducing PAWSmin — and a Defense of Box Score Statistics
Finally, A Guide to Evaluating Models contains useful hints on how to interpret and evaluate statistical models.
Wages of Wins Journal 
Ray
December 22, 2009
Going back to your last post/comments. Jeff Dunham? I read a blog who gets inspired by Jeff Dunham? Now, we’ve crunched the numbers. The comedians WP48 goes as followed (comedians production are consistent over time).
Patton Oswalt: .347 WP48 21.5 Laughs Produced
Michael Ian Black: .243 WP48 11.8 Laughs Produced
Raw and Delirious: .410 WP48 28.9 Laughs Produced
Jeff Dunham: -.118 WP48 -4.5 Laughs Produced
The lesson as always: Economists tend to overrate ventriloquists, well ignoring comedy efficiency. Maybe Dunham isn’t the answer.
dberri
December 22, 2009
Ray,
This is so wrong. Dunham is hilarious. Not quite Jim Gaffigan. But he is up there.
bobbyknightdeathgrip
December 22, 2009
becoming a starter has gone to ariza’s head.
Tommy
December 22, 2009
You’ve missed the fact that the Rockets still have a 16-11 record with the hardest schedule in the entire NBA. They are in the playoffs with that schedule. After January 1, everything only gets easier for them, so it’s unlikely their win percentage will decline and more likely it will increase.
brgulker
December 22, 2009
I’m hoping that some commenters who’ve watched the Rockets play more than I have could offer some guesses as to why Ariza is shooting below career averages.
I watched LA quite a bit last season, and it seemed to me that Ariza benefited from playing there, as most of his shots were created for him by teammates and the defensive adjustments that other teams made to account for Kobe, Gasol, and even Odom.
It’s been my tentative, working theory that Ariza has been asked to not only take more shots, but to be responsible for creating more of those shots for himself, which has led to a decrease in efficiency.
But the thing is, I have no idea how one would test that. We could potentially look at how many of his FGs were assisted last year vs. this year? Maybe we could look at where on the court he’s taking his shots (maybe more inside last year vs outside this year)?
But it seems to me that Ariza is a case worth thinking about. I’d love to hear what others think.
brgulker
December 22, 2009
forgot to subscribe…
izzy
December 22, 2009
brgulker–you are exactly right. It is the type of shots that Ariza takes that cause his efficiency to decline. Not only is he being asked to take more shots, but as you said, he isn’t playing alongside as many offensive superstars that create easy looks for him. That’s why WoW isn’t the end-all be-all. It doesn’t a player’s role into account. Ariza is in a different place with different responsibilities.
Ray
December 22, 2009
David, we can agree on Gaffigan, but god Dunham sucks.
Anyway, here’s your numbers on Ariza’s creation this and thats. Last season shot jumpers 56% of the time, with an eFG of 42%, 78% assited (!). He shot 62.5 eFG% in the paint the remaining 44% of his shots, which were assisted 54% of the time.
This year, he’s shooting jumpers 69% of the time (+13 %) on just 64% assisted, to an eFG of 38.6. He goes inside only 34% of the time now, with only a eFG% of 58, with 46% assisted.
So, he’s shooting more jumpers, creating his own shot more, and upped his usage rate from 16.7% to 23.2%. So, Ariza has unwisely become more of a jump shooter, and has likely seen a drop to a lack of assited looks. He really needs to go inside more, use his athletism. He has a paltry foul-drawing rate, even if he’s a suspect free throw shooter, it’d help his game. Usage increase only affects efficiency a little bit, so this is all on Ariza’s poor shot selection.
Sam
December 22, 2009
Wow, Carl Landry is so good you listed him as above average twice!
KC
December 22, 2009
I’ll 3rd brgulker’s point. Ariza is playing a different role on this team and that has changed the nature of the shots he’s getting. I have not seen enough of the R’s to know if this new role is the coaches’ doing or something in his head that has him thinking he’s The Man. Reminds me of Stephen Jackson’s time on the Warriors. When the offense stalls and teamwork fails to yield a shot, the ball ends up in SJ or TA’ s hands and they have to create something, usually into the teeth of the D.
This does suggest some interesting questions to study — like what impact trades have on player’s WP performance, or WP performance versus contract calendars.
simulator
December 22, 2009
If such data that Ray posted (assisted %, jumper/inside scoring %, etc.) are available, then it’d certainly be worth including them in future research endeavors in analyzing a player’s effectiveness.
Although WoW is decent, I feel that there are a lot of data (whether recorded or not recorded) that it simply does not take into account.
Maybe most players post consistent numbers because their roles are pretty similar from year to year.
However, cases like Ariza’s occasionally happen in games where a player’s role changes quite dramatically, as represented by the shooting rate, assisted rate, mins played, etc. And I doubt that WoW studies have taken those into account.
AlmightyJ
December 22, 2009
Mr. Berri, I find the Rockets an interesting contrast to the Chicago Bulls, who seem to have completely fallen apart following the departure of their primary scorer (Ben Gordon), an admittedly and acknowledged below average player.
I’ve watched most of their games this year and it seems that the players are struggling to pick up the scoring burden. The statistical part of my brain screams that it shouldn’t be the case, but it looks like Ben Gordon was a good fit for the Bulls, as currently constructed, because he was better at taking the bad shots than the other players (John Salmon, Derek Rose) who have been asked to pick up the slack.
Do you have an explanation for their cover-your-eyes, hide-the women-and-children-awful start to the season? Is Vinny Del Negro really that bad of a coach (I know, I know. Coaches don’t matter that much, but is he one of the outliers?)? Are we dealing with too small of a sample size?
I’m at a loss…
TBall
December 22, 2009
I think Ariza’s noted decline in shooting efficiency could conceptually correlate with Josh Smith’s increased efficiency early this season. It all goes to discretion, recognizing your strengths, and choosing to take higher efficiency shots. Josh Smith started the season making that commitment while Ariza may have committed to simply shooting more.
Ray’s numbers would back this up. According to Ray, Ariza is taking a whopping 69% of his shot attempts as jump shots, while 44% are within the paint, indicating he is taking 103% of his available shots. As a rule, no one should ever take more than 100% of their shot attempts. Share that other 3% with the rest of the team.
It is the mid-range part of his game that is giving Ariza the most difficulty, as his 3-pt shooting has improved this season (to 34%) and has advanced from 32% of his FGA to 38% of his FGA. His eFG% from beyond the arc is .509. Taking this information and other data (from basketball-reference and 82games) and his close/mid-range (within the arc and outside the range 82games defines as ‘close’)/3pt eFG%’s are approximately .58/.23/.51. Maybe it is time to show more discretion in that mid-range game.
For what it is worth, 82games is also showing Ariza’s eFG is materially better when playing SF (and suggests he’s been spending more time at SG this year). I don’t know if Ariza has more trouble with smaller, quicker defenders or if this is the result of small sample size, but I suspect a position change (SF to SG) can cause some decline in eFG%.
Ray
December 22, 2009
TBall, I think you were being funny, but I laughed when I read that second paragraph. That was a typo. 69% of jumpers this season, 31% in the paint (not 34).
Sorry everybody, just a mistake. So when that math didn’t add up to 100, it’s 69 that was correct, and 34 was wrong.
Italian Stallion
December 22, 2009
“If a statistical study suggests otherwise, it must be missing something.”
I made that statement and stand by it.
In fact, I think it’s so obviously correct, I can’t believe anyone that has ever played basketball disagrees with it.
IMO, the only debate is how much changes in usage impact efficiency, when, at what extremes of change it becomes easy to measure, and how we should measure it.
IMO, the first key point to understanding this is that the more a player increases his usage the greater the demands on his skill set are typically going to be.
For example, let’s use a post player without much shooting range (not unusual).
If he limits himself to dunks and lay-ups he can get “X” shots per 36 and do very well.
If a team focuses on getting him more dunks and lay-ups, they can probably increase “X” somewhat without altering efficiency, but there is a limit to that increase because the defense will try to prevent those very efficient shots. (We also know from observation that no team can get all dunks and lay-ups. Not even Wilt could when he dominated) .
If the player/team wants to increase “X” further than that, the player is going to have to take some shots further away from the basket, against double teams, or add some other slightly more difficult shots.
Those shots will typically be lower percentage shots as we know from various studies on shot success from various locations.
Then he will run up against the natural limit of that group and have to move further out etc…
The point at which that player/team should stop trying to increase “X” is where his efficiency falls below average ON THE NEW GROUP (key point) and/or when there are superior alternatives available on the team .
We also know that the more offensive skills a player has, the wider variety of shots he can make at adequate rates. (for example Larry Bird vs. Renaldo Balkman lol)
So we can conclude that great offensive players can increase “X” with little or no negative impact to Adjusted FG% MUCH better than poor offensive players (but even great ones eventually run up against their limit)
Coaches attempt to keep players within their limits and the players are constantly trying to increase their limits so their usage can rise and they can remain as efficient (then they make more money).
That’s the way basketball actually works!
The second part is measuring the impact.
As I suggested above, because we are talking about individual players with different offensive skill sets, there is probably no formula that is going to apply equally to all players!
Second, at any given time we don’t know how far any given player is away from his maximum potential/usage because he could easily be under or over utilized in any snapshot in time.
(An example of this might be the Celtics. They have so many great players there are probably several on that team that could easily increase their usage with little or no negative impact).
Third, because players are always trying to increase their skill set, variations in usage that seem to have no impact on efficiency could actually be measuring changes in skill and not suggesting that usage doesn’t matter.
So trying to create a formula for this OBVIOUS BASKETBALL REALITY is probably beyond anyone, let alone a basketball observer like me. ;)
However, I think an observation of the range of a player’s skills can help determine whether he can increase usage.
Looking at the detailed stats of how effective he is from various spots on the floor can help etc…
Finally, I’d like to point out how hard it is notice the impact even when it’s clearly there.
1. Assume a player has an adjusted FG% of 50% on his current mix of shots and takes 10 shots per 36 minutes.
Now let’s say he increases his shot attempts by 5 (or a whopping 50%).
If he shoots 45% on those incremental shots it changes his OVERALL Adj FG% to 48.3%.
If he shoots 40% on those incremental shots it changes his OVERALL Adj FG% to 46.7%.
That’s hardly even noticeable DESPITE a huge 50% increase in usage. So it could easily be written off to randomness, be impacted by randomness in the opposite way, or be seen as not particularly significant.
HOWEVER, the important point is that actual decrease in efficiency on the INCREMENTAL SHOTS was quite huge (a 10% drop and 5% drop) compared to the original group.
I said right after the Ariza trade that I expected his efficiency to drop if they upped his usage significantly because he’s not a particularly good outside shooter yet (even though he CLEARLY has been improving with time) and because he was recently benefiting from a couple of wide open looks per game as a result of playing with Kobe. I saw no way to increase his usage significantly and remain as efficient UNLESS he became a better outside shooter (which was possible because he is young and has been improving his outside shot)
IF I WERE TO ANALYZE ANOTHER PLAYER, I might conclude that he COULD EASILY INCREASE USAGE and REMAIN AS EFFICIENT.
THERE IS NO EASY FORMULA when player skill sets are different, usage levels are different, skill levels are changing, and players might be under or over utilized at any given time.
(REMEMBER, comparing old Adj FG% to new Adj FG% masks the impact. You have to look at the Adj FG% on the incremental shots, but that’s a very difficult thing to isolate without very detailed stats).
Italian Stallion
December 22, 2009
Sorry for the long post, but this is a very difficult topic to explain even though it’s easy one to understand if you’ve ever played the game.
dberri
December 22, 2009
IS,
I would argue that everyone — including me — has played the game. And that will be the last time you press the cap keys on a post.
Italian Stallion
December 22, 2009
I haven’t seen a lot of Rockets games or the studied the breakdown of everything he’s doing, but it sounds like you guys are doing a great job of explaining the decline in his efficiency.
I am seeing the opposite effect in NY now. I am a huge Knicks fan and watch every game.
Every Knicks fan on earth has been getting a sore throat for the last 1 1/4 years from screaming at Wilson Chandler during each game.
He’s not a terrible player, but his shot selection has been atrocious for awhile now and early this year it actually got worse. So his efficiency was becoming a nightmare.
About a month ago either D’Antoni finally put on reins on him and/or he finally figured it out.
He lowered his attempts from beyond the arc, (where he’s bad unless wide open from certain spots), sharply reduced his shots from just inside the arc (where he is bad and only gets 2 points if he makes it) and is now going to the hoop more often (a skill he’s had all along but underutilized badly).
As a result his efficiency in December shot up sharply from Oct/Nov this year and last year even though he retained similar usage – just as every Knicks fan has known it would for the last 15 months. Uggh.
I would guess that could easily be related to being asked to play a lot of SG.
Italian Stallion
December 22, 2009
D Berri,
I’m not sure what the problem is with “very selective” use of caps when trying to emphasize a point.
I don’t know how to change font or bold letters etc…
I would never use all caps (shout) and will refrain from using any caps at all in the future.
Can I change the font, bold, or use italics like above .. for emphasis?
dberri
December 22, 2009
IS,
Why not just say what you have to say and leave it at that? All caps is annoying and doesn’t help you make your point.
psych432crossculturalblog
December 22, 2009
I think Ariza is just playing out of position at SG. It reminds me of Kevin Durants rookie year when PJ Carlislimo used him at SG and he shot like 41%. Anecdotal example of coure.
Rob O'Malley
December 22, 2009
Sorry, I dont know why it keeps signing me in under that account.
Tim
December 22, 2009
dberri — just out of curiosity, do you believe a statistician could be as effective as an epidemiologist in the study of incidence rates and their causal relationships?
(no caps used here, so i’m clearly being very polite)
Joseph
December 23, 2009
as noted above – take a look at the percentage of shots Ariza takes that are assisted and compare it to last season as a Laker. I regressed assists on fg% and found that they do have a significant impact…
Paul
December 23, 2009
dberri,
I think this is a much stronger challenge to your existing model than you are willing to grant. Four points, and the fourth one’s the biggy:
1) The alternative theory of shooting efficiency predicts that Ariza’s shooting percentage would fall relative to what it was on the lakers, not relative to his career average. You are playing fast and loose with the alternative hypothesis here.
2) Ron Artest has experienced a comparable increase in shooting efficiency after performing the inverse of Ariza’s move, in fact they have more or less switched efficiency numbers. This is consistent with the alternative hypothesis, but needs to be explained as random variation within your model.
3) Ariza’s team mates have not moved from the Lakers to the Rockets, so the alternative efficiency hypothesis would not predict similar declines for them as for Ariza.
4) You do not have a data set of observations of a natural experiment where players’ shooting volume varies while holding their ability constant. What you have is a large set of observations for shooting volumes as allocated by coaches who are attempting to optimise efficiency. This makes the vast majority of your data set useless for the purpose for which you are applying it here. You need to look for natural experiments where a pre-selected player is placed in a situation that would tend to change their usage rate even where their talent remains constant.
Artest and Ariza represent only two such data points, but they are, at present, 100% of the relevant data set, not, as you suggest, a tiny fraction of it, because the data you have is corrupted by the fact that it is selected from an underlying universe of potential shot-distributions by an intermediate third party attempting to influence the variable you are trying to measure.
I’ll second Italian Stallion that some means of emphasises key phrases would be nice. Can I just use textile?
Chicago Tim
December 23, 2009
I know you normally conclude that coaching is overrated, but I wonder if Phil Jackson had something to do with Ariza’s better than usual performance last year and whether Vinny Del Negro has something to do with the Bulls’ worse than usual performance this year.
TBall
December 24, 2009
Chicago Tim,
db’s analysis has shown that players see virtually no material change in WP48 when they change teams/coaches, outside of the normal year-to-year variation. He did list a few coaching exceptions and one of them was Phil Jackson.
A fraction of Ariza’s decline could be assigned to the change in coaches, but Ariza’s decline (and it is still a small sample size) exceeds the variation db normally assigns to these coaching exceptions.