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Advanced stats say Zaza Pachulia is the NBA's 4th-best center. Well ...

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Pachulia's been great for the Mavericks, but ESPN's RPM stat might overrate his impact.

Kevin Jairaj-USA TODAY Sports

When the Mavericks acquired Zaza Pachulia via trade this summer, he was the backup plan's backup plan. DeAndre Jordan's eleventh hour change of heart in free agency denied Dallas a chance to pursue remaining free agent centers, so they settled for a player who had been only a part-time starter throughout his career.

Five months later, Pachulia is averaging a double-double for a Mavericks' team off to a surprising 9-6 start. He also ranks fourth among centers in ESPN's Real Plus-Minus (RPM) ratings, the first batch of which were released earlier this week.

NBA fans and observers have an assortment of advanced stats available through with which to analyze the games. The RPM rating was created as a more sophisticated version of traditional box score plus-minus stats, which reflects how much a player's team outscores (or is outscored by) an opponent when he is on the floor. But a player's plus-minus can reflect who they share the court with as much much more than their own production.

Setting aside a disappointing road trip this week, the initial numbers for 2015-16 do a fair job reflecting lessons from the eye test this season -- the Mavericks' old, unathletic frontcourt has kept the team afloat through the first quarter of the season. Highly paid wings Chandler Parsons and Wesley Matthews have predictably been slowed by injuries suffered last season and those struggles are reflected in their poor ratings. Dirk Nowitzki, meanwhile, is having a bounce back year and Pachulia has been better than even his teammates expected.

Nowitzki's 3.79 RPM rating (No. 13 overall) ranks fourth among power forwards, behind only Draymond Green, Paul Millsap and Kevin Love. Pachulia's 3.48 rating (No. 17 overall) play ranks behind only Tim Duncan, DeAndre Jordan and Andre Drummond at his position.

One notable aspect of their RPM ratings is how they complement the other's respective strengths. Pachulia has had a much bigger impact on the defensive end, where Nowitzki has struggled mightily in recent years.

RPM isn't a perfect stat. Any single metric for an individual player's performance is going to have its limitations. Maybe the best example from Dallas is how Jae Crowder ranked No. 9 among all NBA small forwards when ESPN introduced the metric the spring 2014. Jonathan Tjarks detailed at Mavs Moneyball back then how Crowder epitomized the problems with the metric -- it still doesn't completely remove the noise of teammates' contributions. From Tjarks:

What this is really showing you is why (Rick) Carlisle is such a good coach. He doesn't do rotations in broad strokes -- he has very distinct combinations of players he uses for very small periods of time for very specific reasons.

Crowder wasn't really asked to do anything special in reserve lineups other than play passable defense, move the ball and occasionally hit open shots. Carlisle has done an excellent job of putting role players like Jae in a position to succeed in Dallas. Brandan Wright, a reserve who was heavily used in lineups with Crowder, put up All-Star caliber Player Efficiency Ratings for three and a half seasons as a backup center with the Mavericks. But Wright never played more than 18.7 minutes per game with the team and there's no question his elite level advanced stats had a lot to do with playing against other backups in units anchored by Nowitzki.

Advanced stats like PER and RPM, while fun to use in arguments, don't take account of teammate quality in these lineups.

What's impressive about Zaza's RPM score -- and his career-best 18.3 PER -- is that he's having such a positive impact while playing as a full-time starter. Pachulia is also averaging the most minutes per game since his third year in the league.

The only other Maverick to rank in the top 50 for RPM scores is second-year power forward Dwight Powell (No. 45 overall with a 2.03 rating), another Dallas role player who has surprised many with his production so far this season.

But the Dallas bigs aren't suddenly better players than guys like Tyson Chandler, who left for Phoenix this summer while Dallas pursued Jordan. For one thing, the stat counts defensive and offensive impact equally. And Chandler's ability to score at the basket can simply change the game for an opposing defense -- a fact not reflected in RPM. For a deeper look at the limitations of the metric, check out this post from The Corner Three.

The stat should still be taken with a grain of salt and used as an evaluation tool along with the eye test. Pachulia's strong defense has been a pleasant surprise this season but he's never been the rim protector Chandler is. His skills as a passer and midrange jump shooter are big positives for Dallas. But he's not a threat rolling to the rim and catching lobs on the offensive end. That's why the team is so hopeful JaVale McGee can make a comeback as an NBA player this season.

RPM is likely to vary widely for individual players -- both during the season and year-to-year. So it's to be expected that some kind of drop off will occur. But for NBA observers who haven't been paying attention to Dallas so far, the first set of RPM numbers is revealing of the kind of impact Pachulia and Nowitzki have had for the Mavericks even after many wrote them off as big time contributors.