The Same Story for Chris Paul and the Need for a New Trevor Ariza

Posted on December 30, 2010 by


About a month ago an Ian Thomsen story appeared in Sports Illustrated detailing the resurgent New Orleans Hornets.  At the Huffington Post – again, about a month ago — I took issue with Thomsen’s story.  For Thomsen, the story was all about changes to both the team’s roster and the team’s front office.  This focus, though, struck me as largely misplaced.  It seemed to me that the numbers suggested the big story was Chris Paul getting healthy.

Chris Paul and Not Much Else

Okay, another month has passed (as I mentioned).  And now we can see that all the changes the Hornets have made – to both the roster and front office – haven’t really made a difference.  After 32 games, the Hornets have scored 101.8 points per 100 possessions while allowing 100.2.  The team’s efficiency differential – offensive efficiency minus defensive efficiency — of 1.62 is consistent with a team that will win about 45 games across a full season.  Yes, this is better than what we saw last year.  But this is not much of an improvement.  In sum, it doesn’t look like the Hornets – despite all the changes to the roster and the front office – are ready to contend for an NBA title.

When we move from efficiency differential to Wins Produced, we can see why this team is not quite a contender.  As the following table notes, Chris Paul is really very, very, good.  In fact, Paul is once again among the leaders in the NBA in Wins Produced.  And as noted a few weeks ago, Paul is also the primary source of this team’s improvement. Unfortunately – despite all the changes to this team (did I mention, changes to both the roster and front office?) – Paul is still not getting much help.

David West and Emeka Okafor – two of the only four teammates Paul has left from last year – are above average this season (average WP48 – or Wins Produced per 48 minutes — is 0.100).  And that result is not much different from last year.

Unfortunately, the rest of the roster is below average.  And this result is really not that surprising.  The Hornets added eleven new faces.  So far, all eleven are below average players.  Ten of these players played in the NBA last year, and when we look at what each player did in 2009-10 we see that only Jarrett Jack was above average.  In other words, it’s not a surprise that so far the Hornets have struck-out with these additions. 

The Hornets experience appears to put an interesting twist on what was observed about the Detroit Pistons about two weeks ago.  The Pistons – as has been noted before – brought back essentially the same players this year and are getting essentially the same result.   Each time this is noted (and it has been noted more than once) it is argued that players are quite consistent in the NBA.  So if you want your results to change, you need to employ different players.

The Hornets experience this year suggests an addition to this rule.  Specifically, if you want your results to change, you need to employ “better” players. 

And until the Hornets find “better” players, the tragedy of Chris Paul (like the tragedy of Kevin Garnett observed once upon a time in Minnesota) will continue. 

Trevor Ariza and the Usage Story

One player the Hornets added was Trevor Ariza.  In the past Ariza has been above average.  Last year, though, Ariza went to the Houston Rockets and saw his production drop.  Fans of the “usage” argument immediately cited Ariza as evidence that the “usage” story is correct.  Just to review… the usage story is that players who see their shot attempts rise will see their shooting efficiency decline.  Last season, Ariza saw his shot attempts rise with Houston — and just as the usage folks expected — Ariza’s shooting efficiency dropped.  So naturally, the usage story was clearly confirmed.

Last year I noted, though, that a number of other players saw their shot attempts rise with the Rockets and their shooting efficiency didn’t really decline.  In response to this observation, though, people argued that all that matters is what happened to Ariza (yes, people really made such an argument).  Apparently, you only need one piece of evidence to believe a story.

Obviously I found this story unconvincing.  And this is because I have actually looked at the link between shot attempts and shooting efficiency. 

Here is what we say in Stumbling on Wins (p. 206):

The key issue in looking at scoring is not shots taken but shooting efficiency. It’s thought that a player who takes more shots will see his shooting efficiency decline. If you regress shooting efficiency—measured with points per shot or adjusted field goal percentage—on shot attempts you do not see this relationship. However, if you look at the link between the change in a player’s shooting efficiency from season to season and the change in his per-minute shot attempts, the expected link is seen. The effect, though, is small. To see how small, 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%. This is a very large increase in shot attempts, but it only appears to reduce shooting efficiency by about 1%. Consequently, players have a clear incentive to shoot as much as they can. Even large increases in shot attempts don’t diminish efficiency very much. But such increases do add to scoring totals, and more scoring will lead to more minutes, money, and fame. One should note that there is no statistical link between a player’s shooting efficiency and the shooting efficiency of his teammates. In other words, playing with teammates who tend to hit their shots will not make a player a more efficient shooter.

The above paragraph reviews a study that looked at thirty years of player data (and thousands of observations). Although such a study might be convincing, we all know that all that matters is Trevor Ariza.  And this year Ariza  — relative to what we saw in 2009-10 – is taking fewer shots.  Again, the usage story is that fewer shots will lead to increases in shooting efficiency.  So we should not be surprised that Ariza’s shooting efficiency has suddenly… okay, it has actually gone down a bit more.

Wait, that can’t be right.  The usage story is that fewer shot attempts leads to much better shooting efficiency.  Again, we see there is a link between shot attempts and efficiency, but it is quite small.  Ariza’s performance is not even consistent with even the small effect we uncover (and that is because the changes in the number of shots a player takes doesn’t explain much of the change in a player’s shooting efficiency) .  And Ariza’s performance in 2010-11 is certainly inconsistent with the usage story people trumpeted last year.

Hopefully, though, another player will start taking more shots in the NBA and see his shooting efficiency decline (or take fewer shots and see his efficiency rise).  Again, fans of the usage argument only need one anecdote to run with.  So let the search begin for a new poster child of the usage argument!!  Surely we can find someone to take the place Trevor Ariza has unfortunately abandoned.

– DJ