The law developed by an Italian economist in the 1800s based on the principle that the vast majority of an end result (wealth, cost, quality problems, etc.) is determined by a small percentage of a group (the number of people, items, etc.) Often stated as the 80/20 rule, it is used in inventory counting and quality systems to concentrate attention on the small (20%) number of sources that account for 80% of inventory value or quality issues.