A Peek Behind the Curtain

Posted by Rob Mahoney on March 10, 2010 under Commentary | 15 Comments to Read

I’ve received a handful of emails and comments over the last week or so asking me to chime in on the Mavs’ surprisingly low standing in John Hollinger’s power rankings. For the most part I’ve stayed away from it, and for two reasons:

  1. They’re power rankings. No offense to John or Marc Stein or anyone else who compiles power rankings anywhere on the internet, but they just don’t interest me. They’re arbitrary descriptors of how teams have done over the last week or so with emphasis on ranking rather than analysis. There’s just not much you can do with a short blurb that’s going to shed much light on a team’s success. If you dig power rankings, then by all means. I just don’t like getting too caught up in which team is put where.
  2. Unlike other power rankings, Hollinger’s are completely transparent. He spells out his methods explicitly, even giving you the exact formula by which his rankings are calculated, and the reasoning behind the weighting of each of the factors. He also explains why he chose specific measures over others, and the whole process is based on plugging numerical data into Hollinger’s equation.

Given those two things, I’m not exactly sure what all of the fuss is about. The Mavs have been winning games, but not all of the wins have been convincing. Nail-biters over teams like the Wolves and the Heat are not going to boost the Mavs’ standing in a data-centric ranking system, unless it’s completely dependent on win-loss record. Hollinger’s rankings are not, and he tells us as such in his explanation.

Instead, he looks to point differential, which just about any source will tell you is a better indicator of future success than overall win-loss record. Although talent and performance are definitely factors, close games are more likely to be influenced by luck; a bounce of the ball here or there can completely shift the balance, and though it’s certainly impressive that the Mavs are able to execute in high-pressure situations, it’s not necessarily all that indicative of the Mavs being a dominant team. Cue Kevin Pelton of Basketball Prospectus:

Better teams definitely tend to win more close games than weak ones, but the relationship is hardly perfect. The correlation is just .454 (a correlation of 1 or -1 means two variables are perfectly in sync, while a correlation of 0 means no relationship whatsoever). There are two extreme schools of thought on close games–those that believe they are primarily decided by luck and those that feel they are primarily decided by teams and demonstrate their true ability. Neither position is supported by the data.

Instead, what the results tend to show is that the difference between good teams and bad teams is mitigated in close games. Look at the best-fit regression line on the chart. The slope is nowhere near 1, and the difference between the expected record in close games for the very best teams (about .600) and the very worst teams (about .400) is much smaller than the difference between them in games that are not decided down the stretch.

When you think about it, this makes perfect sense. Say you were coaching (or cheering on, if you prefer) an underdog team playing a powerful opponent. If I gave you the opportunity to advance directly to the final five minutes of a close game, even if you were trailing by a couple of points, you would take that scenario because anything could happen over the shorter period. The same logic can be applied to explain why we see more upsets in the one-and-done NCAA Tournament than in the NBA’s best-of-seven postseason. The smaller sample draws all teams toward .500.

The data just doesn’t support the idea that better teams perform better in close games in any kind of conclusive fashion, for exactly the reasons that Pelton describes. It’s still bloody impressive that the Mavs have been able to win 12 games in a row, but it would obviously be more impressive if every win came by way of a double-digit margin.

As you well know, they haven’t. Most have been competitive well into the fourth quarter if not until the very end, and that certainly doesn’t reflect well on the Mavs.

Even given their recent tear, the Mavs’ point differential isn’t receiving any kind of considerable bump. Wins are obviously more helpful than losses in that regard, but it’s not as if a six-point win over the Bulls or a five-point win over the Bobcats is going to make some kind of profound impact on their overall standing. Dallas has overtaken Denver and is headed towards L.A. in terms of win-loss, but they very nearly snatched the record for consecutive wins by an unimpressive margin.

That may be enough to score brownie points with the likes of you, I, and Stein, but the numbers aren’t so kind. Hollinger warns us of that very thing in the explanation of his methods:

Since this is an entirely automated ranking, you’ll notice certain “human” factors missing. It doesn’t know which players are about to come back from injury or which teams have been playing without their best players for the past 10 games. Along the same lines, it doesn’t take into account injuries, trades, controversial calls or any other variables — just the scores, please. Nonetheless, it can be very useful because it allows us to see what the landscape looks like when we remove our usual filters. [Ed. note: Emphasis mine]

It’s not accounting for the fact that Erick Dampier has been out of the lineup, that Brendan Haywood has missed games due to injury, that Jason Terry underwent facial surgery, and that all the while, Caron Butler and Haywood are still integrating themselves into the system. Those aren’t critiques of Hollinger or his work, merely the system. They’re limitations he doesn’t try to hide or obscure in any way, just things that can’t really be taken into account mathematically.

Plus, looking to the methods again:

…I weigh a team’s full-season results by two-thirds and its most recent games by another one-third, so the overall ranking gives greater weight to recent games. You’re probably wondering at this point what I mean by “recent.” It varies depending on where we are in the season. For the first 40 games of the season, it means a team’s past 10 games. From that point forward, however, it means the most recent 25 percent of a team’s schedule. The net result is that, after the first 40 games, a team’s most recent 25 percent of its schedule will account for 40 percent of its ranking. [Ed. note: Again, emphasis mine.]

The last 25% of the Mavs’ games are more heavily weighted for the purposes of the rankings, and that’s a big part of the reason why Dallas is ranked so low. You’d think that the winning streak would off-set the rest of that 25% sample, but it just doesn’t. Dallas is 10th in point differential (+3.06) over that stretch, but the real kicker may be their strength of schedule: the winning percentage of the Mavs’ opponents over the last 25% of games is just .467, which ranks 23rd in the league. Given the weakness in Dallas’ point differential (10th) and strength of schedule (12th) overall, what did everyone honestly expect would happen in the midst of a 12-game winning streak in which all but one win have been by 10 points or fewer?

The Mavs are still a work in progress. We don’t yet have an accurate grasp of how the defense will perform with two healthy centers, or what kind of rhythm the offense can get into with all hands on deck. So the fact that Dallas is 9th in offensive efficiency and 12th in defensive efficiency, while hardly heart-warming, doesn’t really distress me. We likely won’t have an accurate macro statistical picture of this team going into the playoffs, because the data from earlier in the season is practically defunct given the roster moves, and the game data available offers a pretty small sample size.

These Mavs are contenders. They’re not on the level of the Lakers and are probably only on equal footing with the Nuggets, but that puts them in a position to do serious damage. I guess that’s where my views really diverge from Hollinger’s…or at least his views from about a week ago. All of the Mavs’ problems haven’t miraculously disappeared nor have all of their weakness morphed into strengths. But I think they’re good enough to beat the Nuggets in a seven game series, and good enough to give the Lakers a run for their money. If that’s not contending in the West, then what is?