# Pareto chart

Simple example of a Pareto chart using hypothetical data showing the relative frequency of reasons for arriving late at work.

A Pareto chart is a special type of bar chart where the values being plotted are arranged in descending order. The graph is accompanied by a line graph which shows the cumulative totals of each category, left to right. The chart is named after Vilfredo Pareto, and its use in quality assurance was popularized by Joseph M. Juran and Kaoru Ishikawa.

The Pareto chart is one of the seven basic tools of quality control, which include the histogram, Pareto chart, check sheet, control chart, cause-and-effect diagram, flowchart, and scatter diagram. These charts can be generated in Microsoft Office or OpenOffice as well as many free software tools found online.

Typically on the left vertical axis is frequency of occurrence, but it can alternatively represent cost or other important unit of measure. The right vertical axis is the cumulative percentage of the total number of occurrences, total cost, or total of the particular unit of measure; because the reasons are in decreasing order, the cumulative function is a concave function. The purpose is to highlight the most important among a (typically large) set of factors. In quality control, the Pareto chart often represents the most common sources of defects, the highest occurring type of defect, or the most frequent reasons for customer complaints, etc.

The Pareto chart was developed to illustrate the 80-20 Rule — that 80 percent of the problems stem from 20 percent of the various causes.