Offensive Impacts

EDIT/UPDATE: This old formula has some truth to it, but I have a much more accurate method of describing this, as described in the College Basketball Prospectus 2011-201 book.

There's a very simple stat that estimates how much a player affects their team's overall offensive rating, using Dean Oliver's Individual Offensive Rating (as is posted for all teams' significant players on Kenpom.com)

Formula for offensive impact =
team ORTG - (team ORTG-(%poss*%min*ORTG))/(1-%poss*%min)

(Which estimates the impact a player has on his team's overall Offensive Rating)

Here it is for UNC and Duke:

North Carolina	player	%Min	ORtg	%Poss	offensive impact
	Tyler Zeller	69.4	119.2	23.4	3.93
	Reggie Bullock	32.2	106.3	20.7	0.54
	Justin Watts	29.4	106.1	14.8	0.34
	Leslie McDonald	35.3	97.7	18.7	-0.06
	Kendall Marshall	35.9	95.5	19.2	-0.23
	Harrison Barnes	69.4	96.8	22.9	-0.34
	Justin Knox	37.2	93.9	24	-0.46
	Dexter Strickland	62.8	93.7	17	-0.58
	John Henson	61.6	94.6	25.5	-0.74
	Larry Drew	63.8	76.8	14.6	-2.21
Duke	player	%Min	ORtg	%Poss	offensive impact
	Kyrie Irving	72.2	128.8	25.2	3.12
	Andre Dawkins	57.8	144.3	13.2	2.44
	Seth Curry	44.1	117.3	18	0.22
	Ryan Kelly	35.9	116	13.5	0.07
	Tyler Thornton	12.8	88.7	13.3	-0.45
	Nolan Smith	76.6	113	27.5	-0.45
	Josh Hairston	14.4	90.5	13	-0.46
	Kyle Singler	78.8	112.1	21.2	-0.52
	Miles Plumlee	36.6	90.3	17.8	-1.69
	Mason Plumlee	66.3	101.6	21	-2.11

Now these stats don't exactly compare (a player with a +2 on a bad team is not as good as a player with +2 on a good team) - but this allows you to estimate what current substitutions do for a team, offensively (per 100 possessions).