 This idea is sometimes expressed more simply as the Pareto principle or the "80-20 rule" which says that 20% of the population controls 80% of the wealth.However, the 80-20 rule corresponds to a particular value of "α", and in fact, Pareto's data on British income taxes in his "Cours d'économie politique" indicates that about 30% of the population had about 70% of the income.The probability density function (PDF) graph at the beginning of this article shows that the "probability" or fraction of the population that owns a small amount of wealth per person is rather high, and then decreases steadily as wealth increases.