ROI on articles

Ages ago, when Associated Content was not Yahoo Voice, someone somewhere said that for each dollar spent on article, AC earned 8 dollars from ads in one year.

My question for those into blogging is, have you tried to calculate your ROI and if you could, without revealing your niche, share what ROI you got per published 100 words or similar metric?

I never did that, Its good point. I do keep track of all the expenses I spend on my sites.