The Pareto principle, simply stated, is that 80% of problems are produced by 20% of the possible causes (80/20 rule).
A Pareto chart is a bar graph. It is used to rank categories from most to least significant. The lengths of the bars represent frequency or cost (time or money), and are arranged with longest bars on the left and the shortest to the right. In this way, the chart visually depicts which situations are more significant.
Use a Pareto chart when analyzing data about the frequency of causes in a process or when communicating with others about your data. Pareto charts may be helpful in displaying data presented for management review.