This article was originally published on SI.com

If you want to know the offensive value of Gilbert Arenas or Tyson Chandler, take a look in the box score published in any newspaper. If you want to know their defensive contributions, enter the Twilight Zone of opinion and guesswork. That is, until now.

For years, defensive statistics haven't painted an accurate picture of individual performance. Blocks, steals and defensive rebounds are useful, but don't cover much of what good defenders do. Roland Beech at 82games.com provides useful "on/off" data: measures of what the team does when an individual player is in the lineup vs. when he's not. That information tells a lot about a player's impact, but it doesn't tell us why.

For example, a fan might look up Wizards center Brendan Haywood's on/off information and find the Wizards are nearly 10 points better per 100 possessions defensively when Haywood is on the court. Only five other players with significant playing time -- Tim Duncan, Andrei Kirilenko, Dikembe Mutombo, Jason Collins and Jeff Foster -- have on/off impacts as large. But there's no way to know whether Haywood's "impact" is real or whether it's luck.

To answer that "real vs. luck" question, defensive statistics were collected possession-by-possession and shed considerable light on what individual players are doing on the defensive end. Categories include individual shooting statistics (field-goals allowed and forced misses), forced turnovers that aren't steals and fouls resulting in free throws.

This data collection yields intriguing information about the Bulls-Wizards playoff series. Game 4 hero Juan Dixon was the Game 2 goat -- but not because of his 3-of-12 shooting. Dixon was the proverbial gas on the fire, allowing scores on 12 of the 13 possessions for which he was at least partly responsible. The Bulls scored 27 points on those 13 possessions en route to a 113-103 win and a 2-0 series lead.

Dixon scored a career-high 35 points in Game 4, and was once again a defensive sieve. The Bulls shot 7-of-16 against Dixon, including 4-of-8 from 3-point range, and totaled 22 points against the diminutive guard.

While Dixon has been picked on throughout the series, both teams have had outstanding individual defensive performances. For Bulls fans, this is probably a common experience -- Chicago had the league's second-best regular-season defense behind the San Antonio Spurs. Wizards fans have heard about defense, and even witnessed it on occasion -- usually played by the other team. In their first playoff appearance since the '90s, the Wizards appear to be learning the importance of defense.

For the series, Chicago has held Washington to 42.1 percent shooting from the floor. The Bulls' defensive star -- when he's been able to stay out of foul trouble -- has been Chandler. Against him, the Wizards are shooting just 32.5 percent and he has nine blocks in four games.

Antonio Davis has also done a good job forcing misses. The Wizards are shooting 36.3 percent against his defense.

Andres Nocioni was outstanding in the first three games of the series, drawing four charges and collecting defensive rebounds like Dennis Rodman. Despite pedestrian defensive play from Nocioni in Game 4, Washington is shooting just 39.1 percent against him for the series.

For the Wizards, the individual defensive numbers range from the expected to the surprising. During the season, Haywood was best on the team at forcing misses -- opponents shot 32.8 percent. That has continued in the playoffs; the Bulls are shooting just 36.5 percent against Haywood. As a team, the Bulls are shooting 41 percent against the Wizards.

Larry Hughes, who contributed during the regular season with steals and defensive rebounds, also is doing a better job of forcing misses in the playoffs. For the season, opponents shot 47.5 percent against Hughes -- the Bulls are shooting 36.7 percent. Hughes also is tied for the team lead in defensive rebounds (23) with Arenas and Antawn Jamison.

Arenas, who was defensively erratic during the regular season, has been a pleasant surprise after a rocky Game 1. He was responsible for forcing 6.5 turnovers in Game 3, and is the series leader in forced turnovers (steals plus non-steal forced turnovers) with 15.5.

The data collection goes into significantly more detail than what gets summarized in the box scores.

Shots are tracked in three ways: contested, open and wide-open. These category definitions have been refined through conversations with current and former NBA coaches, front-office personnel and players. This allows a detailed look at how individual offensive players perform against different kinds of defense.

For example, the standard box score shows Ben Gordon's Game 1 shooting as 11-of-19 from the floor and 3-of-5 from 3-point range. The defensive stat collection shows a more detailed line:

Ben Gordon's Game 1 Shooting

Contested Shots

FG -- 4
FGA -- 9
3FG -- 0
3FGA -- 2

Open/Wide-open Shots

FG -- 7
FGA -- 10
3FG -- 3
3FGA -- 3

The defensive stats collection also highlights the uselessness of a common method for rating individual defenders: studying counterpart box-score stats. In theory it makes sense -- Arenas and Chicago's Kirk Hinrich are both point guards, so looking at what each does offensively should offer insight into what the other does defensively. Except in practice, it doesn't.

Such analysis ignores that NBA teams use an array of defenses, including various zones (the Wizards use at least three in the half-court), and an astonishing array of nuanced man-to-man schemes. Defenders switch constantly and every NBA team expects every man on the floor to help.

For example, in Game 4, eight different Bulls were responsible for the outcome of at least one of Arenas' offensive possessions, not counting three possessions which couldn't be assigned to any particular players. Hinrich did most of the work, accounting for seven possessions -- but that was less than a third of Arenas' possessions.

This kind of data collection will continue throughout the playoffs, and may be expanded next season. It won't end the argument over who really is the best defender, but it's at least some new ammunition for the battle.

Kevin Broom is a senior writer at RealGM.com and columnist for WizFans.com. He can be reached at kevinbroom@realgm.com.