Like all formulas, it has its pros and cons, but what makes this formula interesting is that at Hoops Stats you can break down performance by position, or by bench or starters. Applying this formula to the Bulls bench, then, allows for a detailed comparison between this year's and last year's respective units.
Overall, on the season in 2011-12, the Bulls bench outperformed their counterparts 45 of 70 times (with two draws), and that was in spite of the fact they had to step up and fill in for 84 different starts in only 72 total games.
If you look at games where the Bulls had their full starting lineup, the bench outperformed their counterparts 11 of 15 times, and the Bulls were 13-2 in those games. (Starting lineup dates were obtained from basketball-reference.com and then compared against the Hoopstats data).
The Bulls did not lose a single game when they were at full strength and their bench outplayed the opponent's bench. That's how good they were.
This year, the Bench Mob has not been so successful. They've been outworked by their opponents much more frequently, as they have won the contest against their opponents only 20 times in 36 tries. That's a "winning percentage" of just .556 this year compared to .638 last year.
It's worth noting that it's still better than half the time, which is telling. They win more than half their contests and are ranked 17th in the NBA, So, the Bulls bench so far can be considered average to above-average in terms of their performance. That's better than many expected.
However, looking at some whole numbers gives more perspective. First look at what the Bulls did last year versus this year (in terms of whole numbers) compared to what their opponents did.
A cursory look would suggest that the Bulls are being ever so slightly outworked this year by their opponents compared to last year. They give up 1.7 more points, 1.5 more rebounds and are even on steals and assists. They give up a smidgen on rebounds, and they have a slightly lower efficiency.
However, look at the first number, the minutes, and you see a very revealing number. Their opponents are playing 12.8 more minutes per game. Opponents played more minutes last year too, but not as much as this year.
The Bulls bench actually outworked their opponents in spite of the fact that they gave up 3.4 minutes per contest. This year they're playing nearly even despite the fact they are logging 12.8 fewer minutes. Here's a look at what happens if we adjust the numbers per 48 minutes.
Adjusted per 48 minutes, there are two things that are apparent. First, the Bulls are doing better against their opponents while they're on the court this year than the whole numbers suggest. It indicates that perhaps the primary thing that the Bulls are missing this year compared to last year is minutes.
The second is that the thing they miss the most is Omer Asik. In the rebounding department, while their bench decisively won the battle of the boards last year, this year they're barely winning it. They're getting 1.6 fewer rebounds per 48 minutes this year, as well as half a block. All of that screams Asik.
Essentially, the only true center other than Noah whom the Bulls have this year is Nazr Mohammed, who has been, at best, marginally effective in spot play, but he has been worlds apart from Asik.
What gets more interesting is the recent trend. Look at the last 10 games compared with the Bulls bench last season, adjusted per 48 minutes.
While the Bulls are still playing fewer minutes than their opponents, they are playing more minutes over the last 10 games than they were for the first half of the season. Also, they are beginning to correspond more with last year's squad.
In fact, per minute, they are actually outscoring last year's squad, getting the same number of assists and getting more steals. Last year's team still does better at rebounding and shot-blocking.
The Bulls may be looking to add one more player before the trade deadline. It they could make that player a more reliable backup center, it would be a "big asset," pun intended.
Apart from that, the main thing coach Tom Thibodeau needs to do to improve his bench is what he's already started doing—play them. As the Bulls bench plays more and plays better, they're going to move up the ladder.
Over the last 10 games, they're 11th in the NBA. As they continue to gel and adjust to Thibodeau's defensive system, the minutes will come and the team will improve. Nothing yet on whether that reliable center is on the way, but one can only hope.