The Pareto Principle

The history of the 80-20 Rule: Vilfredo Pareto (1848-1923) was an Italian economist who, in 1906, observed that twenty percent of the Italian people owned eighty percent of their country's accumulated wealth. Over time, this theory came to be called Pareto's Principle. It states that a small number of causes is responsible for a large percentage of the effect, in a ratio of about 20:80.

comments at Signal v. Noise.