Pareto Diagram

The Pareto diagram is a graphical overview of the process problems, in ranking order of the most frequent, down to the least frequent, in descending order from left to right. Thus, the Pareto diagram illustrates the frequency of fault types. Using a Pareto, you can decide which fault is the most serious or most frequent offender.

The basic underlying rule behind Pareto's law is that in almost every case, 80% of the total problems incurred are caused by 20% of the problem cause types; such as people, machines, parts, processes, and other factors related to the production of the product. Therefore, by concentrating on the major problems first, you can eliminate the majority of your problems. The few items that have the largest amount of occurrence are your more frequent problem, than they are many items that only happen once in a while. This is called the "few vital over many trivial" rule. Quite often, once you cure several of the "big hitters" you also eliminate some of the smaller problems at the same time.

So then, what exactly is a Pareto diagram?

The Pareto prioritizes problem areas. Sometimes a quality problem is so cluttered with so many smaller problems; that it makes it difficult to know just where to begin the solving process.

Let's take an example:

This table from is a manufacturing process that charted all of their quality problems.

While the original defect chart listed many problems at various stages of the process, the overall problems were grouped into five main process areas. In the left column is the name of the process where the defects occur.

In the next column is the amount of defects recorded from their daily check sheets, recorded during a one week period. In the third column is the percent of defectives from the overall production (N = 2165).

In the fourth and final column, is the percent of the total defects. That is, for example, of all the defects recorded (416), poor Caulking is 47.6% of the entire problem. It should be obvious then, where the primary problem is and what should be focused upon first. 

This is the Pareto for the example case were you can see that caulking is the one that has the biggest column. 

The left vertical border shows the number of defects for each defective category, and the right vertical border shows the percentage of each defect of the total defects.

The horizontal bottom lists the defective items starting with the most frequent one on the left (Caulking), progressing over to the least frequent occurrence on the right side (Torque).

Therefore, the Pareto diagram visually indicates which problem should be solved first, or in this case, the Caulking problem. With this bar graph, it is easier to see which defects are most important of all the defects that exist. If we solve all or most of the problems in Caulking, it could affect some of the problems observed in connecting, gapping, fitting, and torque.

Bibliography

The quality, W. (27 de Agosto de 2010). Beginner's Guide: The 7 basic quality tools. Recuperado el 2 de Noviembre de 2013, de http://thequalityweb.com/pareto.html