About 30 years ago a mathematician working at my employer told me about Pareto’s Law or principle and how it worked. I had recalled learning about the theory in college but never had an opportunity to apply its use.
The theory was devised by Vilfredo Pareto. In 1906, the Italian economist created a mathematical formula to describe the unequal distribution of wealth in his country, observing that twenty percent of the people owned eighty percent of the wealth. The Pareto law, in its generalized form, states that 80 % of the objectives – or more generally the effects – are achieved with 20 % of the means – or more. In other words, not always in the exact 80/20 ratio, this phenomenon seems to occur in many venues.
If you apply the principle to the distribution of wealth in the United States you reach the conclusion that about 20% of the population does own 80% of the wealth. Although it is not precise, G. William Domhoff’s research about America’s wealth distribution seems to hold up fairly well.
Back at the factory I worked in 30 years ago the sales of our 110 unit product line did break down to 80% of the revenue coming from 20% if the items we offered. It was almost exactly in that ratio. I was astonished how closely the numbers were aligned.
I am willing to bet that 80% of the revenue in any super market is derived from 20% of the stocked items plus or minus 3%.
Coast Contact 
You might be interested in this post: http://lvtfan.typepad.com/lvtfans_blog/2008/03/the-8020-rule-.html
One might think about the possibility that 20% of America’s land contains 80% of the land value — I have no proof of that, but certainly know that urban land value is hundreds of thousands of times the value, per acre, of good agricultural land.
Those who own our best land collect the rent on it from their fellow human beings. As I read in someone’s sigfile, that gives them the capacity to collect the value of thousands of people’s wages, for value they didn’t create. And then those same people must pay taxes on their wages, on their purchases, their buildings, etc., in order to fund the very services which make that urban land so valuable. (Think about the federal dollars which flow to our big cities, and the aid NYC gets from NYS.)
Think, too, about who gets the value of the world’s nonrenewable natural resources. The corporations … their shareholders … their top management … who tend to be in the top 5% of our income and wealth distributions. (The same blog has a number of posts about income and wealth distribution, with 2007 Survey of Consumer Finances data.
Are our corporations entitled to the value of our urban land, our natural resources? Or are we all equally entitled to that value, having been created equal?