Dak Prescott and Carson Wentz have both been winning rookies, but Prescott's performance has been superior. USA TODAY Sports, Icon Sportswire

The raw passing numbers of rookies Dak Prescott of the Dallas Cowboys and Carson Wentz of the Philadelphia Eagles look fairly similar:

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Prescott: 68.7 completion percentage, 7 passing touchdowns, 1 interception, 103.9 passer rating

Wentz: 63.8 completion percentage, 8 passing touchdowns, 3 interceptions, 92.7 passer rating

But through the lens of Total QBR, a significant difference emerges. Prescott leads the league with an 82.9 QBR, while Wentz ranks 29th with a 49.9. Both quarterbacks have been good enough to win (the Cowboys are 5-1 heading into their Sunday night showdown against the 4-2 Eagles), so where do the differences in their performances lie?

Context is key

Total QBR is opponent-adjusted, so a good performance against a bad defense is weighed as such. Wentz's numbers are hurt by the fact that he's faced the easiest set of QBR defenses in the league thus far.

For example, in Week 1, Wentz had an unadjusted QBR of 66.1, which looks pretty good by itself, but if we take into account that it came at home, the opponent was the Cleveland Browns and that it was the second-lowest opponent QBR allowed by the Browns this season, it gets adjusted down to a 53.2 -- just about average. This isn't isolated to just the Browns game. Wentz has the lowest QBR allowed by the Lions and the Redskins as well. A look at the strength of Wentz's performances for each team Philadelphia has played:

Week Opponent Wentz Raw QBR Rank among QBs faced 1 Browns 66.1 6th of 7 2 Bears 58.8 5th of 7 3 Steelers 78.9 2nd of 7 5 Lions 58.9 7th of 7 6 Redskins 30.7 7th of 7 7 Vikings 13.0 4th of 6

Prescott has also faced a fairly easy set of opponents (28th easiest of 31 qualified quarterbacks) but has exceeded what other quarterbacks have done against those defenses:

Week Opponent Prescott Raw QBR Rank among QBs faced 1 Giants 60.2 4th of 7 2 Redskins 88.2 2nd of 7 3 Bears 98.8 1st of 7 4 49ers 84.7 2nd of 7 5 Bengals 87.5 1st of 7 6 Packers 70.4 2nd of 6

It's worth noting that the duo shares a pair of common games so far, having both played Washington and Chicago. In both cases, Prescott had a vastly superior raw QBR (98.8 to 58.8 against Chicago and 88.2 to 30.7 against Washington) to Wentz.

Moving the chains on third down

One big spot in which Prescott has separated himself from Wentz is third down. Prescott has the sixth-best raw QBR on third down, with a 72.0, while Wentz ranks 22nd with a 36.8.

The big driver here is their conversion rates when passing. Both have converted their only third-down scramble attempt and have taken five sacks apiece, but when they do throw on that down, Prescott has converted 48 percent of his attempts into first downs, where Wentz has converted only 35 percent of his attempts -- less than the league average of nearly 40 percent.

Overall Prescott is completing 73.1 percent of his third-down pass attempts, best of any quarterback in the league, while Wentz is connecting at a 56.3 percent rate, slightly less than the league average (59.4 percent).

Carson Wentz third-down chart Hank Gargiulo/ESPN

Dak Prescott third-down chart Hank Gargiulo/ESPN

Wentz reliant on short passes

No qualified quarterback has a higher percentage of pass attempts come on screen plays than Wentz at 16 percent, and only Matthew Stafford has attempted more screen passes overall (32 to Wentz's 29). Wentz also has the second-highest percent of attempts at or behind the line of scrimmage of qualified quarterbacks, slightly behind Alex Smith at 27.6 percent.

These shorter passes by design are set up to help the quarterback, and QBR takes that into account when dividing credit on the play. So when Wentz connects with running back Darren Sproles 5 or 6 yards behind the line of scrimmage and Sproles ends up with a big gain, most of the credit there is given to Sproles and the offensive line, not Wentz. Meanwhile, Prescott is in the bottom third of the league in passes at or behind the line of scrimmage, with just 17 percent of his attempts in that range, less than the league average of 20.7 percent.

When we add everything up, we see that Wentz has not outplayed other quarterbacks who have faced the same defenses, is not converting third downs at a high rate and is reliant on having his receivers make plays for him on short passes, all in contrast to Prescott.

All of the above tells the QBR story -- even if the raw numbers and team records would suggest the players are equal.