The real stars of the season so far

— -- If the NBA season were a school year, we'd already be handing out first-quarter grades this week. So which players would deserve an A-plus for their early work in the 2014-15 campaign?

To address such questions, Jeremias Engelmann and I introduced an advanced metric last season: real plus-minus (RPM). It's a mathematical estimate of each player's true plus-minus contribution, adjusting for the strength of every on-court teammate and opponent. RPM gauges the impact of each player on his team's net efficiency (points per 100 possessions). And it yields separate metrics for offensive (ORPM) and defensive (DRPM) play, respectively.

From RPM, we can also generate wins above replacement (WAR), which takes into account each player's total possessions to estimate the number of wins he's generated for his team (above and beyond that of the typical " replacement player").

Here's the current RPM/WAR leaderboard:

It's not a bad list of All-NBA candidates through the season's first quarter. It also suggests some provocative takeaways, among them:

Harden's new commitment to defense appears to be real -- and it makes him a legitimate MVP candidate

James Harden's matador defense is the stuff of legend, not to mention viral YouTube videos. According to RPM, his reputation for atrocious D last season was fully justified: His defensive RPM value (minus-2.84) was among the league's worst. Even his brilliant offensive play couldn't completely offset the damage, as he was nowhere to be found among last season's total RPM leaders.

But Harden is one of several players -- together with DeMarcus Cousins, Rudy Gay, and Kyrie Irving -- who have taken their respective games to a whole new level after spending the summer with Mike Krzyzewski, Tom Thibodeau and the rest of the Team USA staff. And while no one is ever going to confuse the Bearded One with Tony Allen, it's clear that Harden has elevated his defensive play this season.

You can see it in the box score stats, where he has suddenly emerged as one of the game's most prolific shot-blockers in the backcourt (third among guards at 1.1 blocks per game) and climbed into the league's top 10 in steals (2.0 per game). You can see it even more clearly in his defensive RPM rating this season (1.82), quantitative evidence of a dramatic turnaround in overall defensive play.

On the strength of such improvement, Harden has quietly posted the second-highest WAR in the league thus far, and propelled the Rockets to their red-hot 16-5 start this season.