Pareto Chart

Posted on February 9, 2009 by

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The Pareto Chart (also called Pareto Diagram) is used to show the various causes of defects. It is listed as a tool and technique of the fourth edition PMBOK®’s Perform Quality Control process. The purpose of the Pareto Chart is to identify the biggest problems affecting quality so that those causes may be targeted for improvement first. This concept is based on Pareto’s Law (also called the 80/20 rule) which is applied in this context to state that 80% of the problems are due to 20% of the causes. The various causes of defects in a Pareto Chart are ordered from left to right starting with the biggest cause of defects. The exception to this is the “other” category which is always at the far right. If the first several bars are substantially larger than the others, it is called a Pareto Effect. Note that if the “Other” category is comparatively large, it warrants further investigation to determine whether there are some major causes of defects that need to be further investigated. Pareto Charts typically display the number or percentage of defects, and some also have a line above the bars illustrating the cumulative percentage of the causes of defects.

Pareto Chart

Pareto Chart