By Andrew Mooney, Boston.com Correspondent

The American League Most Valuable Player will be determined in the coming weeks, and the Red Sox boast three candidates — Adrian Gonzalez, Dustin Pedroia, and Jacoby Ellsbury — who will receive significant consideration. There’s not much argument that Gonzalez and Pedroia have been the most valuable at their respective positions league-wide, but the same can’t be said for Ellsbury. Is he even the most valuable center fielder in his own division?

The challenger to that label, of course, is the Yankees’ Curtis Granderson. The tutelage of hitting coach Kevin Long appears to have injected new life into his swing, which has shown unprecedented power this season. Let’s see how the two players stack up at the plate.

Jacoby Ellsbury
.313 BA, .371 OBP, .526 SLG, 169 hits, 97 runs, 44 BB, 24 HR, 84 RBI, 85 SO, 36 SB

Curtis Granderson
.273 BA, .375 OBP, .584 SLG, 135 hits, 123 runs, 75 BB, 38 HR, 107 RBI, 144 SO, 24 SB

Offensively, the edge has to go to Granderson. His explosion in power numbers — second in the majors in home runs and fourth in slugging — is a more than favorable tradeoff with his high number of strikeouts. He also draws significantly more walks than Ellsbury, translating into a higher on-base percentage despite a batting average 40 points lower. Though it’s hard to find many flaws in Ellsbury's season thus far, the Red Sox might like their lead-off hitter to sport a walk rate closer to that of Kevin Youkilis than Carl Crawford.

But a look at our old friend Runs Created reveals that the disparity is not as large as might be supposed; Granderson maintains only a slight 111 to 107 advantage. Though Granderson’s homer totals are flashy, Ellsbury has steadily racked up the singles and doubles — more valuable for run creation than his counterpart’s walks — and kept his strikeout levels in check. Factor in the greater threat he poses on the base paths, and the gap between the two begins to look very small indeed.

On the defensive side, things get a bit murkier. Many advanced metrics, like FanGraphs’ Ultimate Zone Rating (UZR), rate Ellsbury as the top center fielder in the majors — not too surprising given his exceptional range. Yet by the same measures, Granderson, who made a name as a highlight reel defender in Detroit, ranks as one of the worst. A variety of theories have been proposed to explain this: perhaps fleet-footed left fielder Brett Gardner covers a good chunk of his territory in left-center; he may indeed have lost a step; or advanced defensive statistics are the domain of the occult.

Sabermetricians say stats like UZR are better measured over three-year periods; single-season numbers may be skewed by small sample-size bias. Over their last three full seasons, the numbers still heavily favor Ellsbury — his three-year UZR is 27.3 (runs saved above average), compared to Granderson’s -0.8. Even allowing for a substantial margin of error, it looks like Granderson has regressed from his early days as a Tiger, where his ’05-’07 UZR was a healthy 30.6. Ellsbury has indeed been superior in the field.

It’s this discrepancy that accounts for Ellsbury’s slim lead (6.5 to 5.5) in Wins Above Replacement (WAR), an overall measure of player value that’s gaining increasing importance in the MVP voting. When the defensive component is removed from the statistic, Granderson (5.7) is deemed more valuable than Ellsbury (5.2).

So making a judgment here depends on one’s perception of the respective defensive abilities of Ellsbury and Granderson. Trusting the data, Ellsbury has been better overall; Granderson may make a few Web Gems, but the subtle things, like taking good routes to fly balls, are much more important in a consistently good center fielder. Not that this could ever be said of a certain other well-regarded Yankee defender…

For my part, I believe Granderson’s decline in the field isn’t as drastic as UZR would have us believe. His workload in center has indeed been cut down by the presence of the speedy Gardner, artificially reducing the value of his defense. And to answer those who attribute his high power totals to the short porch in Yankee Stadium, he’s actually produced nearly identical numbers on the road as at home. While Ellsbury has provided virtually everything the Sox can ask for from the lead-off spot, Granderson’s been the more valuable player in 2011.

Now, if you’ll excuse me, I have an angry mob to outrun.